Strange pop-up in the Taskbar Windows XP

[#1]

I have been getting a strange pop-up in the XP Taskbar recently.  I do not know what it is, have never seen it before and do not seem to be able to get rid of it.  It does not appear to be harmful (but you never know) but I cannot find out what it is associated with.  Can anyone help ?
It just pops up every hour or so and closes down before I have a chance to do anything about it.  I have tried to hide it in Taskbar Properties, but it is not registered.  I have tried looking also in the Task Manager but cannot recognise anything under Processes which might be related.  But all those svchost.exe files could mean anything - how do you get more detail on them ?
Anyway, this morning, acting extremely quickly, I managed to do a screen dump before it had time to close - my fingers happened to be in the right place.  From that, I have managed to crop an image of the offender, which I attach.
Does anyone recognise this or know what it might be ?  There are no clues except the exclamation mark, the mouse and some other icon.
Any ideas would be appreciated.  See attached screen dump.

[#2]

I have never seen this before but my guess would be that you have a wireless mouse and the pop-up is trying to tell you it needs a new battery.

[#3]

:-[Thank you ReedRichards for stating the blindingly obvious.  I am certain that you are absolutely right.  I do indeed have a wireless mouse and now you mention it, I suppose that other icon on the right is meant to be a battery, nearly empty !  How stupid could I be ?  The reason is of course that I was expecting something malicious and therefore could not look beyond the end of my nose.  Thank you very much for putting my mind at rest.
I have never seen this pop-up before, even though I have had to change the battery a number of times.  The software for the cordless mouse and keyboard has been a pain generally.  I regularly get balloons telling me that various function keys are active and I cannot turn them off - even the manufacturers have no solution.  I can turn them off by setting EnableBalloonTips in the registry to "0" but as soon as I re-boot, the software re-sets it to "1".
Anyway, I cannot thank you enough.  I will now change the battery and hopeful that will be the end of this particular saga.  But this is how to feel stupid in one easy lesson !

[#4]

Quote from: shermans

But all those svchost.exe files could mean anything - how do you get more detail on them ?

Too many could indicate malware or spyware, see here http://www.howtogeek.com/howto/windows-vista/what-is-svchostexe-and-why-is-it-running/
That's only for Vista but there are many other useful links out there, they will all at some point recommend a 'free' download to scan and fix the problem, many, while doing the job will sometimes install one of their own. It's a constant battle, basically steer clear of free tool bars, marketing surveys, and the like, get a good AV product on board, deep scan at the very least once a week.
If you are really confident in your backup regime, save your vital data, reload from scratch your operating system (including a disk reformat, this is only if you are beyond confident in your reload ability, it will take some time, all Windows patches will need to be reloaded, all drivers will need updating etc. etc.), then, check the Task Manager again, you will be amazed.