There is no "SystemC" standard. Remember that SystemC is really just a C++ library (API). Using a common C++ coding standard of which there are several (e.g. JSF) is a good place to start. Here are a few ideas:
Indentation (a hotly debated topic) - I prefer two spaces. Look for tools support to automate this aspect.
Variable names should not be abbreviated, but rather use lowercase and separate words with underscore.
Classes should start with Uppercase letter.
Member data other than channels/sockets, should be prefixed with m_.
Class static variables should be prefixed with s_.
Suffixes should indicate process types (i.e. _thread, _method, _cthread), channels (_channel), events (_event), ports/sockets (_port/_socket).
More importantly, if you are going to use a standard, there should be a tool that can help enforce/code.
WARNING: You might want to avoid any standard suggesting leading underscores and a few other things. See the following Stack Overflow article for a discussion of this <http://stackoverflow.com/questions/228783/what-are-the-rules-about-using-an-underscore-in-a-c-identifier>.