I use the eight dollar extension [1]. Basically it replaces the blue verified tick with a dollar sign for paid accounts. I started using it when there was a still a mix of old verified and new paid accounts, both of which were given the same verified sign by twitter, but I kept it even after because it feels more truthful to reality, as it just informs that one has paid to twitter. I think this should be the default.

[1] https://addons.mozilla.org/en-US/firefox/addon/eightdollars/