For example, keywords have a special prefix. Objective-C has @interface, @implementation, but that's for compatibility with C. It inherits all the C keywords of course, with no @. How about a language in which all keywords are prefixed with a special character? It'll save the lexer some trivial trouble, but the programmer finally gets to use the words float, class, template ... etc.

Or the countrary, user defined names must be prefixed with a special character.

Are there (popular) languages that do either?