Good save.
It's an LMR type VHF antenna, usable for 2m through 174mhz depending on whip length.
For 2m you'll probably need a 48" whip or thereabouts. Maybe 48 1/2. I usually end up taking off about 1/2 or 3/4 inch from an NMO150.
Antenna analyzer is of course very helpful but here's the Larsen cutting chart:
https://www.repeater-builder.com/antenna/pdf/larsencuttingcharts.pdfPO150 is on page 13. If you measure the whip the chart will get you relatively close to what it was cut for.
The color & details can give you an idea of how old the antenna is. If you post a pic of it we could estimate the vintage
The nut on top of the plastic base is threaded, normal right hand thread if you want to remove it, can also loosen the little set screw and remove the whip from the nut. Some of them are hollow so that the whip can extend down into the base slightly which makes tuning easier.
As far as another band, as previously mentioned that base has a coil inside which would probably make it unsuitable for higher frequency operation, but it would work on 6 meters if you're willing to experiment with whip length. Different brands 5/8 wave mobile antennas generally resonate somewhere in the 6m band as a slightly base loaded 1/4 wave, but getting them to work as a dual-band antenna can be a challenge. Magnet mount vs permanent mount alters the 6m tuning noticeably (as with any 6m mobile antenna).