Siscia 52 is unusual because of the obverse legend which is IMP CONSTANTINVS MAX AVG. This is the only time MAX is used for a VLPP from Siscia. This coin is also noted from a single example in RIC. A few years ago I got an example of this type, but the style was not right. I had it tested and it turned out it had circa 2% silver, versus the 4% silver it should have had. This further led me to believe that this coin was an unofficial issue. I started thinking that maybe the one example cited in RIC was also unofficial. The example was from the Nagyteteny Hoard (which I believe contained quite a few unofficial issues).
The first coin below is Siscia 52 and the second one is Siscia 54. These two coins were issued about the same time.
Edit- I have found another example of RIC 52
http://www.lateromanbronzecoinforum.com/index.php?topic=575.0
