What two separator characters would work in a URL anchor?

Question

I use anchors in my URLs, allowing people to bookmark 'active pages' in a web application. I used anchors because they fit easily within the GWT history mechanism.

My existing implementation encodes navigation and data information into the anchor, separated by the '-' character. I.e. creating anchors like #location-location-key-value-key-value

Other than the fact that negative values (like -1) cause serious parsing problems, it works, but now I've found that having two separator characters would be better. Also, givin the negative number issue, I'd like to ditch using '-'.

What other characters work in a URL anchor that won't interfere with the URL or its GET params? How stable will these be in the future?