That Thunderbolt is no longer there, it used to sit up there rusting away (rather quickly too) on top of a county building across from Madison Square. The T-bolt quit sometime in either the late 90s or early 2000s according to Chatham County EMA, and I guess they finally found someone to remove it from its perch. It was an old Series A1 1000A (not a "jailbar"), and I actually got to hear it once as a kid while we were on River Street, which is also when I found out about the Model 2 next to the river by surprise.
On a side note, they have been slowly replacing a lot of the old sirens in Savannah and the rest of the county over the past few years with Whelen Vortexes, but their main goal has been to add new ones to fill in the existing coverage gaps first. They still have a couple of 2T22s, a few STH-10s (most on buildings), and at least that one Model 2 next to Moran Towing.
-Ian M.