One creative idea for a thermometer sign is to create a phrase related to the activity that the thermometer is designed to gauge. For example, a fundraising thermometer may use a phrase such as "Please help all of us fight against leukemia." Give each letter of the phrase a certain dollar amount and, when enough money has been raised, reveal that later. This builds public interest in donating in order to reveal the full phrase.
One idea that is better suited for a digital sign or display is an image of a young boy who is too short to ride a carnival ride. As donations come in, the little boy appears to get taller and taller until he is tall enough to get on the ride, signifying that the fundraising goal has been met.
A seasonal version of the fundraising thermometer involves covering up different sections of a Christmas tree. Similar to the phrase-based thermometer, each section of the tree has a target fundraising goal that, when met, reveals that section of the tree. To complete the Christmas theme, decorate completed sections with Christmas lights, and signify that the fundraising has reached its goal by putting a lighted star at the top of the tree.