Signaling is behavior whose main purpose is to demonstrate to others that you possess some desirable trait. For example, a bird performing an impressive mating display signals that it is healthy and has good genes.
This is a hopelessly narrow definition and should be changed. An agent can signal anything about itself, including undesirable traits such as “I’m not edible” or “I’m batshit crazy violent, don’t mess with me”. So lets first lose the clause “desirable”.
And signals can be costly to the sender but not necessarily. The cost (or more precisely, lower cost to honest signallers and higher cost to pretenders) makes a signal more trustworthy in the cases where the sender may have a motive to cheat. In biology, low cost signalling is still signalling. Mothers’ signals to offspring tend to be pretty low cost for example. The offspring trust their mothers anyway and are incentivized to respond as intended; they have not much to gain from distrusting the mother. Babies’ signals to mothers may be costlier in cases when the mother is likely to abandon some offspring based on their fitness. E.g. possibly human babies pack on so much fat and look so plump so as to signal their high fitness to moms (human mothers are known to selectively abandon infants, unlike chimp mothers, whose infants are not so plump). The lower fitness infants are incentivized to look like they had high fitness, so mothers use a hard-to-fake trait such as fat content to assess fitness.
“I’m batshit crazy violent” obviously has a cost because being violent exposes you to aggression by the ones you attack, but I don’t think it involves the competition element like is present in the previous example. Consider a Northern lapwing singlehandedly attacking a hawk many times bigger than itself: she’s not intending to actually fight the hawk, she’s signalling to the hawk that she’s absolutely crazy and will fight to the death; that, of course, would be uncomfortable and painful to the hawk, so the hawk pretty reliably leaves, when it sees the lapwing coming. (Although sometimes lapwings are still killed by hawks). The signalling behavior here is approaching fast in a menacing manner, but lapwings are not competing with each other and the hawk is not trying to assess which lapwing is most violent; this signal is risky (costly) but it’s not subject to runaway competition and not therefore likely to accelerate into depressingly wasteful levels. It can still be perhaps modelled as a handicap signal like the plump infant example, because the costliness of the behavior is a feature not a bug: the hawk can trust the lapwing’s signal because a lapwing who’s not really willing to risk a fight would not dare to approach a hawk.
The alarm signals to one’s flock (“there’s a predator in the grass”) were already mentioned as not signalling anything about the sender; alarm signals are also costly if they attract the predator to the signaller, but here the cost is a bug that cannot be avoided, it’s not a feature of the signal. (Of course, one may combine alarm signals with status signalling, e.g. in some birds the ones who sound most alarms are the most dominant and respected birds in the group because alarm calling is dangerous and only the fittest birds can afford to do it a lot.)
In conclusion, signalling as used in ecology or economy is so much more diverse than in the quoted definition, I don’t see why it should be so narrow in the Wiki. The narrow meaning may be captured by some other term, such as “fitness signals”, “signals of high quality”, or suchlike.
This is a hopelessly narrow definition and should be changed. An agent can signal anything about itself, including undesirable traits such as “I’m not edible” or “I’m batshit crazy violent, don’t mess with me”. So lets first lose the clause “desirable”.
And signals can be costly to the sender but not necessarily. The cost (or more precisely, lower cost to honest signallers and higher cost to pretenders) makes a signal more trustworthy in the cases where the sender may have a motive to cheat. In biology, low cost signalling is still signalling. Mothers’ signals to offspring tend to be pretty low cost for example. The offspring trust their mothers anyway and are incentivized to respond as intended; they have not much to gain from distrusting the mother. Babies’ signals to mothers may be costlier in cases when the mother is likely to abandon some offspring based on their fitness. E.g. possibly human babies pack on so much fat and look so plump so as to signal their high fitness to moms (human mothers are known to selectively abandon infants, unlike chimp mothers, whose infants are not so plump). The lower fitness infants are incentivized to look like they had high fitness, so mothers use a hard-to-fake trait such as fat content to assess fitness.
“I’m batshit crazy violent” obviously has a cost because being violent exposes you to aggression by the ones you attack, but I don’t think it involves the competition element like is present in the previous example. Consider a Northern lapwing singlehandedly attacking a hawk many times bigger than itself: she’s not intending to actually fight the hawk, she’s signalling to the hawk that she’s absolutely crazy and will fight to the death; that, of course, would be uncomfortable and painful to the hawk, so the hawk pretty reliably leaves, when it sees the lapwing coming. (Although sometimes lapwings are still killed by hawks). The signalling behavior here is approaching fast in a menacing manner, but lapwings are not competing with each other and the hawk is not trying to assess which lapwing is most violent; this signal is risky (costly) but it’s not subject to runaway competition and not therefore likely to accelerate into depressingly wasteful levels. It can still be perhaps modelled as a handicap signal like the plump infant example, because the costliness of the behavior is a feature not a bug: the hawk can trust the lapwing’s signal because a lapwing who’s not really willing to risk a fight would not dare to approach a hawk.
The alarm signals to one’s flock (“there’s a predator in the grass”) were already mentioned as not signalling anything about the sender; alarm signals are also costly if they attract the predator to the signaller, but here the cost is a bug that cannot be avoided, it’s not a feature of the signal. (Of course, one may combine alarm signals with status signalling, e.g. in some birds the ones who sound most alarms are the most dominant and respected birds in the group because alarm calling is dangerous and only the fittest birds can afford to do it a lot.)
In conclusion, signalling as used in ecology or economy is so much more diverse than in the quoted definition, I don’t see why it should be so narrow in the Wiki. The narrow meaning may be captured by some other term, such as “fitness signals”, “signals of high quality”, or suchlike.