A sign I consider bad for a roleplay is when the GM posts to move on the roleplay after everybody was ready and then only one of the people who had posted before that posts after. Another sign is when you accept A LOT OF CHARACTERS. Though having quite a few people around is great an all, some GMs will get overwhelmed by a large amount of characters going about. The final sign I've seen often enough is when nobody says anything in the OOC for at least a week. At least, anybody who isn't the GM or Co-GM talking in the OOC. If people disappear from the OOC and don't post in the IC then it is going to be a good sign that they have disappeared.