Other issues to watch out for when food, wax, etc. is attached to the part where there is no letters, numbers, etc.
the "tissue box" in halacha;
floor Drain with Hinges or Handle, Shelf in a Bookcase with Hinges, and the Use of a High Riser or Sofa Bed on Shabbos;
Is There a Way to Move a Flower Pot with a Hole in the Bottom?;