I had an address in my sig for a very short time, and obviously never received anything. Most people who do get about a Satoshi's worth from an advertising bot or some forumgoer who thinks 0.0000001 BTC is an acceptable "tip" for service rendered or information provided. Anticipating a miracle from your forum signature isn't worth the disappointment
To get anything substantial from your sig would probably require that you be one of the ultra-trusted, super-rich, early-adopter core type of forum member. Someone who can escrow 50 BTC without batting an eye, or program a new type of wallet for kicks.
TL;DR version -
Most of us don't get anything and never will.