(Remark: I have just looked up the definition of phobia, and I realized that my condition is not a phobia. I don’t feel any fear, just a very strong urge to avoid situations where bugs are crushed around me.)
I don’t think signalling has much to do with my case. Most people find the sight and sound of bugs being crushed repulsive, and my reaction is basically the same, only stronger.
But there is probably a signalling-based explanation of why I let cockroaches go free rather than flushing them down the toilet. Flushing a bug down the toilet doesn’t trigger my aversion at all. But after all the trouble with capturing them (they are very fast), letting them free feels like the proper thing to do, even though it is quite irrational.
The crushing thing might still be related to a signal even if it’s less direct. But it might not as well.
Also, being signalling means it might be less irrational then you think, especially if you’re around non-rationalist humans. Because, they’ll think of you as kinder and trust you more and stuff.