I don't know what this is, but lately it's been showing up in my menu bar. I've dragged it out of the menubar several times now, but it keeps coming back.
Click on it and see if there's a drop-down menu to start. Look in your System Preferences and Startup Items if there's nothing there. It's obviously related to something you've installed, and seems to indicate either a power or signal level.
I have that icon on my menu bar also and it is related to my sprint broadband air card because that is what I use to connect to the internet and get online. I also can disconnect from the internet. I have to connect and disconnect using that icon. DSL and cable internet are not available in my area and the Sprint air card USB modem is what I have to use to connect. Why it appears on your menu bar I have no idea.