It is so annoying, and so inconsiderate, why do people do it? We have had similar problems but not to the same extent, it sounds like you are in a relatively large scheme?
We have had one owner recently who seemed to think it is ok to dump his rubbish wherever he pleases, and throw pieces of meat in the courtyard for his dog. This culminated in three of us confronting him, and him using some disgusting language in response, but he doesn’t do it now.
Some of the things we have done:
1. in the case of tenants moving in or out, you would know which lot they come from, if they dump rubbish photograph it, and have the strata manager send the bill for removal of the rubbish to the agent. At the same time send an email to the strata manager noting that the residents of Lot X have dumped rubbish so you have a record. If it isn’t paid, make sure it is recorded as a debt against the owner.
One thing a friend’s scheme did was require a bond from any owners who rented their units out, to cover this kind of thing. You need a by-law for that.
2. If you see someone doing it, challenge them. It is very difficult to justify when you are caught in the act.
3. Rather than putting a sign up on the notice-board, put signs up where the bins are.
I am not sure if any of that will help, we still have difficulty getting people to understand the recycling bins, surely it can’t be that hard.