In doing some research I read an alarming story about hotel maids-- how hard they work and little they get paid. With the new plush bedding, their work is truly back-breaking.
Tipping etiquette suggests that they should get tipped $1-2 a day per room. The best way of meeting this obligation is to bring a few envelopes along and put a dollar or two in one every day, labeling it "housekeeper," and leaving in a conspicuous place.
If it is unclear whether the money is meant for them, they can't take it. Only about 25% of hotel patrons tip maids.
Maybe you knew all this already. I did not. We always leave a tip on departing, but not enough. We tip restaurant waitstaff 20%, perhaps because my husband and I were both waitstaff for years.
Maybe in Baltimore, the housekeeping staff will remember that those crime writers at Bouchercon were a generous bunch even if a bit rowdy.