If I had to hazard a guess, I would say the majority of picketers at conventions are NOT xjws, but rather Christians from other denominations interested in "saving" JWs. There are very few xJWs who will picket, and most of them do not behave aggressively while doing so.
In 18 months on these boards, I've only known of three people that regularly picket. One had a personal family issue that he picketed over, one targeted the legal corporation rather than the teachings, and one does peaceful protest on a regular basis. I think if there were many ex-JWs out there doing the actual convention picketing we would see a lot more comment about it on these boards. (of course I could have just missed these threads...)
I don't know that I personally would ever hold up a sign in front of an assembly, since I realize how most react. Even the relatively few that would be inclined to engage the picketers in discussion, or read their signs are, for the most part, hesitant of being seen looking or talking. I remember many occasions where some JW from the convention would be approached, and the elders would come barrelling out in groups of 2 or three to "assist" the JW seen talking to the protester.
My dad did security for a few years at conventions when I was a kid, and one of his jobs was to make sure the protesters didn't disrupt things, but they sure did their part also, just watching to make sure noone talked to the protesters.
I think most of us prefer to innoculate non-JW friends and acquaintances against proselytizing by sharing our experience, and to drop hints that might fly under the radar for our JW family/friends. YMMV.