As per http://forum.mikrotik.com/viewtopic.php?t=11532

It would be nice to include something like $sigstr, $sigccq and $sigspd or something in the values available in the hotspot interface.

While I understand that this information is moot given that the user would have to be connected to see it - it can be used to provide recommendations to the user on how to improve a borderline signal. For example they're connected at 1Mbps with a low strength/quality, just enough to bring up the login pages - provide them with a warning that their connection isn't that good with ways on how to improve it.