This Crispus is not in RIC -- this bust type (G2) is not listed for this series and the obverse legend with NOBI is unrecorded for Crispus. This legend is unusual, but the use of NOBI is not unprecedented; it was used for Constantius I (RIC VI London 36a) circa A.D. 300. Perhaps it is an unofficial issue; however, although it is worn, it looks official. It's lighter than other London issues, but it is worn. It should come after London 196.
It is not listed in the London Mint book by Cloke & Toone.
Crispus
A.D. 320-1
17x19mm 2.0gm
IVL CRISPVS NOBI CAES; laureate and cuirassed bust left; spear over right shoulder.
VIRTVS EXERCIT; Standard inscribed VOT/XX with captive seated on ground on either side.
in ex. PLN
RIC VII London --