[Hans M Aus]

Is there a startup application that warns the user that the WLAN is off and waits until it's turned on?

My friends usually turn the WLAN on only when they work with the Mac and sometimes they forget to turn it on again.

[zombie punk]

Well, the wireless signal on the menu bar will be empty, and the internet won't work - is that not enough of a signal?

[Hans M Aus]

For me yes. But I always observer that users sit and wonder why the email doesn't get sent.

[zombie punk]

How about a post-it note saying 'if the internet doesn't work, switch it on over there!'

[seanc]

This can be done in a 'crude' but simple way.

Open text edit, change to a big font, type in your message, take a cropped screenshot using command+shift+4 & save it to somewhere accessible by the user you want to use it for.
Open System Preferences > Accounts > 'User' > Login Items & add the picture you just made to the login items. On every login the picture will open in Preview or picture viewer of your choice, in my case Xee.

[Hans M Aus]

If on startup the Mac finds only other networks, but not a trusted WLAN, the user is asked if he wants to join another network. Wouldn't it also be possible to tell the user that the Mac hasn't found any active WLAN in the area?