This is one of my favorite gifts to make for a teacher or people in a group (like Sunday School, Book Club, etc). When I began making these in 2005, the only good mug available was at Starbucks. It is still one of the best quality mugs. But you can find lovely mugs at Target and other stores as well.
HOW TO MAKE A SIGNATURE MUG
1. Remove the inner liner from the mug.
2. Trace liner on a piece of watercolor paper.
3. Brush water over traced area. Let water soak into paper for just a moment.
4. Brush layers of color. I went subtle with a tad of purple at the bottom, a wash of blue and then a large area of yellow. The watercolor paint I used has glitter in it as well.
5. Let dry. Cut out the new watercolor liner.
6. Put watercolor liner into mug. Trace the bottom over hang and mark where the paper overlaps so you do not get signatures in that area (it would be hidden).
7. Have the children (or group members) sign the mug in the area that will be visible. (Use a sharpie pen.)
8. Put the liner back in the mug and you are done!