C2 r54; Windows XP SP3; FireFox 6.0.1; ATI Radeon HD 4870
<img src="http://dl.dropbox.com/u/36472942/construct/bugs/missinghotspoticon.png" border="0" />
I noticed it a couple days ago and haven't took the time to report it yet.
Edit: Seems to happen when C2 has been running in the background for a while.
I just relaunched it and the hotspot icon displays as usual. But it wasn't the first time the icon was disapearing.