Attributing Vespasian's early issues from Ephesus can be tricky. Unlike the other issues from the mint they were struck without a mint-mark. These rare non mint-mark issues can be difficult to identify because a mint-mark may originally have been present and can be missing either due to die wear or preservation of the piece. when I saw the following piece go up for auction I was sceptical, since there was only one other known specimen of the type! Happily after inspecting the coin in hand I can be certain this is indeed a non mint-mark issue. I gambled and won. Vespasian AR Denarius Ephesus Mint, 69-70 AD RIC 1395 (R3), BMC 430, RSC 248, RPC 805 (1 spec.) Obv: IMP CAES VESPAS AVG; Head of Vespasian, laureate, r. Rev: LIBERI IMP AVG VESPAS; Titus and Domitian veiled, togate, stg. front (heads l.), each with patera Oddly enough, the other specimen of this type in the BM is off-centre and a possible mint-mark could be off flan. Considering it is a unique coin it is certainly well recorded in the major references!
A dealer friend had a few 'different' Vespasians including this reverse but I did not note whether or not it had a mintmark. I hope it did. I was not aware that this was a consideration. I ended up buying a different type from Rome with better metal and more wear than his coin of T and D standing.
Normally mint-marks are not a concern on Flavian denarii. The only mint which made regular use of them was Ephesus. Your dynastic type is from Rome. The Ephesian version of the type has the reverse legend LIBERI IMP AVG VESPAS. Ironically, my example of the Ephesian type is missing a mint-mark (I also have a Titus Caesar from the same issue lacking one). Therefore, I believe the COS III series had a no mint-mark issue. For now I have it catalogued as a variant of RIC 1429.
I wish to make a correction about the BM coin I wrote above. I no longer believe a possible Φ mint-mark is just off flan after viewing a better image of the coin. As can be seen in the photo the beaded border is just visible at 6 o'clock with no trace of a mark in the exergue. So, the BM specimen and my coin make 2 that are known for this undated T&D type lacking a mint mark. If anyone is aware of another please let me know.
Edit: Another example is held by Muenzkabinett in Winterthur Switzerland and was recently analysed for its silver bullion content by K. Butcher and M. Ponting. Bringing the number of specimens I know of to 3.