I can think of two possible approaches off the top of my head. Though they are more examples of what I mean then anything!
1. On the Exit
One, when you look at one of those view blocking paydoors, you see a brief message hinting at how busy it is inside. The message is based on how many characters or PCs in the bar/club. Whatever metric makes sense for staff.
For example, if the count is 0 and I look at the door the message might say something like, "Very few people are passing into or out of the entrance." Maybe if the count is 7 the message is, "Huge numbers of people are flowing into and out of the entrance."
The message will probably never indicate the place is empty or abandoned as we have ambient population. I would also avoid the message listing specific numbers for the same reason. Just a vague message to indicate if the place is quiet, hopping or somewhere in between. To see if it's worth paying one's way in.
2. On the Room
Mostly the same as above. Get a count (PC or PC and NPC). Relate the count to a vague message. But display the message in the room outside the bar/club like flavor text instead of on the door. So as soon as you outside the bar/club it's apparent without even having to look at the door. Maybe the messaging talks about very few people passing in and out of the place or about the bar being so busy the crowd has spilled out into the street.
I think something like this can help new players as well as they can find other players to interact with a bit more easily as the game is providing clues without them have to know how to ask. Heck, I think it would even help veteran players in much the same way!
