Thanks ..
We're also seeing a lot of users starting to use a mobile device access APP called "Tapatalk" which is a front end for vBulletin access.
The OS icon comes up as "unknown" and the agent shows as this:
Mozilla/5.0 Firefox/3.5.6 Tapatalk 2/2.0.3
Perhaps you could add an icon of some sort that shows they posted with Tapatalk?
Here's an icon attached that they use...
Regards,
Doug