Rain leaves no spots or as stated above hardened minerals that are sometimes near impossible to remove. I myself wouldn't touch the sprinklers, even if you think nobody's watching, 5 pairs of eyes are on you. Try talking to the management first, to provide bike only parking suggests they recognize you and want to accomodate you, I'm sure they don't even know about the problem. Motorcycles here in Ohio, or at least around where I'm at are still looked at as annoying things trouble makers ride and motorcycle only parking is VERY rare anywhere, traffic isn't all that bad to the point where they start rewarding folks who ride with special parking, I don't see it changing anytime soon sadly. Now bicycles, bicycles are the new BIG thing, big, big, big.