My question / comment for the OP is:
Are you employed by the BO as a groom/caretaker, or do you, like everyone else, pay monthly to board?
If you WORK for her, then it kinda is YOUR JOB to sweep, empty trash, etc...therefore signs asking others to do what you're being paid for wouldnt, IMO, be smart...For example I'm a night shift charge RN, and not a housekeeping staff person.
Thus, while I too, am in DISBELIEF many nights at the unbelievable messes our inpatients leave for the housekeeping staff to clean up for them, it IS MY JOB, since it's my unit MY UNIT @night, thus my responsibility to keep it tidy, so I do...same thing if you're working for the BO. While people such as ourselves, who almost REQUIRE cleanliness and organization to feel comfy, cannot SEE HOW OTHERS CAN BE SO PIGGY, we have to accept it as part of life and move on.
If you are a paying boarder like everybody else, almost the same answer applies, except here you must understand that they are paying just like you. If they (the "piggies") don't care about a mess...well...they don't have to! In fact, when you chose the barn, @ that time would've been right to decide if you could "tolerate" the state of cleanliness and pick that facility or perhaps another, cleaner one instead. You all are "equals" & no one but the BO AND EMPLOYEES are REQUIRED to sweep/etc...(again, I DO, & AGREE THEY SHOULD WANT TO, BUT MANY PEOPLE ARE LAAAA-ZEEE!) :0(
I personally wouldn't waste much of my precious horse tine sweeping others' crap up. As long as my horse's stall was properly cleaned EVERY DAY, I'd pick up MY MESSES, & unless I found sweeping, etc...around the stable relaxing or got some other personal pay off (cause I guarantee your horse doesn't mind the mess in the walkway, etc...)I'd leave it be and worry about something else.
I've found when I try to micromanage the world others are truly responsible for around me, MY OWN world gets left in the proverbial "dust"...I wouldn't do that to yourself and I'd try to work on sweating the small stuff a little less! Just some friendly (really!) advice to take or leave! :0)
"I'm too busy working on my own grass to notice if yours is greener"