Letterhead Fonts is a nice source of information as well as a supplier of awesomely sign-friendly fonts, many designed by real hand letterers. Choosing letter styles for sign work requires special considerations that are not always necessary in other media.
The following link is to a tutorial about how good design principles should be applied to even small, unimportant copy. It’s brief, but well done.
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This link is just for fun:
signbrad 