I've found symbols in this explanation for a four way switch but I can't find that symbol in any of the online circuit-drawing tools I've looked at.
The best alternate representation I've come up with is:
This was an interesting exercise and demonstrates that a four-way switch is just a DPDT with its outputs cross-connected. However, it's not as clear as I'd like as part of a larger diagram. Does anyone have a better representation, or know an online tool that has the X symbol from the above explanation available?