release vs debug mode

Does anyone know of a way to tell if a compiled binary was compiled in release or debug mode? In other words, I'm looking for a way to tell if a binary has debugging symbols included.

This is for Microsoft's compilers on the Windows platform. Obviously this is not a binary I compiled, so an answer of "check your visual studio settings" doesn't help me.

Open it in a debugger?

Yes. The Win32 Portable Executable (PE) header does usually include at least a debug flag for C/C++ compiled programs. If you have Dependency Walker in your Visual Studio Tools (if not, get it from http://www.dependencywalker.com), it will indicate which linked DLLs are debug builds. The header is how it knows.