Perhaps but such a sign doesn't work. (Ask me how I know.)
This did - at least, it mitigated the clean-up work immensely.
So I run a free coffee station right outside my Beis Midrash, funded entirely (well, almost) on donations. I am constantly cleaning it up because the avadim moshlu bonu have threatened to shut us down if the place is too messy. As a neat-freak, this cleaning is often traumatic for me.
One morning I had the fabulous idea (from Hashem, of course) to put a sign up announcing that from today, every cup costs 1 shekel - but you don't have to pay if you didn't make anything dirty (or cleaned it up).
Even I was surprised that it ACTUALLY WORKED! (I got a few shekel, but mostly, the place was clean...) 
This didn't work, but it was greatly entertaining:
Post this in your local shared kitchen (edit it based on location).
Dear denizens,
In as much as our new kitchen rules initiative has really taken off, we would like to remind those of you who have not been participating thus far about the following protocols we have running here:
We have a great shortage of cups, both plastic and paper. Therefore, we would like everyone to leave their used cups out when they are finished with them. Please leave them (in order of preference) on the floor (to catch spills and prevent the floor from staining), on the table (so that there is a good selection for the next person), on the cabinet or refrigerator door (only if you are also providing a portion of your coffee or tea for the next person as well – they already know to check these places when they are thirsty), inside the sink (if possible, upside down over the drain to prevent the drain from being stained brown and to facilitate the next item), inside the freezer (but only where it will fall out if the door is open – everyone knows to expect this and will open the door carefully), inside the microwave. This list is by no means exhaustive of the many possibilities. UNDER NO CIRCUMSTANCES SHOULD YOU WASTE THE CUP BY THROWING IT IN THE GARBAGE AFTER USE.
We are in the process of staining our sink brown. Please facilitate this process by doing the following: using your dirty tissues or paper towels to stop up the drain, saving the thickest part of your coffee for spilling into the sink (preferably on parts that the faucet does not reach naturally), putting upside down cups in the sink so that whatever is left from your coffee will drain (this has the side effect of preparing the cup for use by the next person). DO NOT USE THE FAUCET TO CLEAN THE SINK, as this will undo years of our hard work.
Please do your best to get liquid or moisture into the coffee and sugar containers. This will enable the next person to take large amounts effortlessly, and save them the time and effort of scooping coffee or sugar several times. You can accomplish this by stirring your drink with a spoon, and then placing the spoon back in the serving container. (A better mehalech entails the sacrifice of a portion of your drink, which is poured into the container. However, we would not ask this of you.)
We love the adventure of not knowing what is coming. Knowing that the milk is fresh and cold is, to be quite frank, boring. Therefore, we would love it if you did not return the milk to the fridge after use, for the possibility of it acquiring some new and exciting flavors. For greater effect, leave it touching the urn so that the change is facilitated. We can hardly wait!
Many of us have difficulty getting into the containers for sugar or coffee. We would be much obliged if you left a portion of sugar and coffee directly on the table for easier access. The more, the better. This is even more effective if wet, as it is easier to scoop off of the table. Also, see the next item.
It is a known fact that 73% of Yeshivaleit do not get enough protein. Although it is a machlokes if ants are nosein taam lfgam, bmakom sakanas nefashos we can be meikil. There remains only the din of bittul issur lechatchila. This problem will be solved by breeding as many ants as possible in the kitchen premises. Although this results in a chazaka which would require one to check everything that one eats or drinks, we believe that it is likely to result in a greater protein intake for everyone. Therefore, please leave as much open food lying about, as well as providing generous amounts of sugar on the table and floor.
Thank you for your … cooperation … in these matters. We hope to constantly improve your kitchen experience.
The Management
