Place a macron over some lowercase letters to distinguish them from uppercase versions. Perhaps useful for base 52 or 62 or 64.
c o p s v w x z
Lowercase L should be drawn with a loop as in cursive, and capital i should have serifs to keep them looking different. The macron over lowercase w is optional if it has curved bottoms like two U's. (Incidentally, we use an apostrophe in the pluralization of u to avoid confusion with the word us.) Lowercase k is somewhat close to capital K, perhaps draw lowercase with a loop as in cursive.
None of the lowercase letters above have ascenders. However, if added, lowercase thorn does, and looks like its uppercase, as does theta.