It means the authors give support (help) to those that use the modification. As for what vBulletin.org uses, it's a custom portal, the thread prefix mod and modifications by a member of staff which have been released here I think:
https://vborg.vbsupport.ru/member.php?u=925
^The stuff he made
And maybe this:
https://vborg.vbsupport.ru/showthrea...+%2Apm%2A+icon
With the image from here:
https://vborg.vbsupport.ru/showthrea...+%2Apm%2A+icon