There's an icon in the upper right corner of the status area of my N900, and I have no idea what it indicates. It looks like the "do not enter" sign for one-way streets, with a curved line and two smaller lines above it. What is it for?
I'm using SimpleBlue D-Theme.

Might it be GSM or 3G connection indicator?

Not sure, because for 3G, it's actually written "3G" underneath the signal strentgh indicator (both to the left of the battery level indicator).
It might have something to do with wireless or bluetooth set to off. The icon's presence is not always consistent, sometimes its gone until a reboot or power-off.

I'm enclosing the partial screenshot now.

Isn't that your Skype/IM status set to "not available" or something like that?

Well
that's the icon indicating that you turned off your WLan
when you switch your wireless connection on it will dissapear , , when connected to a wireless network it will show the wireless icon there , this however is a wireless connection with a "stop" sign , meaning that the wireless is stopped

On my N900 when I turn WiFi off, I don't get that icon.

So I guess it depends on the icon pack you're using.

you may want to switch back to the standard theme. that will make it easier for others to recognize this icon.

Not connected wifi displays no icon. So it`s not only that You are not connected to any wifi but you have wifi modules (kernel) turned off, via "Wi-fi switcher" or "Adv. Interface Switcher".

wifi-switcher?

Thanks, I guess it is wifi switcher after all. I customized my gadget heavily in the beginning, and now it seems I forgot some things (even app icons aren't always intuitive).