That's why I don't use signals at all for poaching. Poaching effectively imo depends on the server being able to serve the ball into the center of the court near the T and there are too many servers at 3.5 and 4.0 who can't do that. Heck, most of the benefit I see of poaching and fake poaching is generating UEs and weak returns by putting doubt into the mind of the returner about where exactly the poacher will be.
When should you serve and volley in doubles? Only when you want to win.