I agree I've found lipstick and noticeable lack of cleanliness on cups and mugs all the time. I've also found half used waterbottles or already opened water bottles in the rooms. The cleaning staff simply puts the complementary signs back on if the bottles look full, or in some cases half empty.

I also had an instance where there was red tooth paste all over the bathroom sink. I then had housekeeping come up to clean it. Not knowing that I needed to specify to the staff that the red gel was the main issue. She cleaned the shower and toilet and then left without touching the toothpaste. So if that's an indication of the true cleanliness, I'd go with one of the suggestions I saw above and keep away from the glasses.