I'll just say, "no", but I'm not really one to spend much time looking for standard ways to do things. I spend all day looking at maps, so if I don't know "the standard way to symbolize" something, how would a general map reader know? Do something that makes sense to you. Show it to someone else. Does it make sense to them? If so, it's probably just fine.
With that said, there just may be a stickler out there that knows how you're "supposed" to do this.