Watch List notes:

Domitian. As Caesar, A.D. 69-81. Æ as (28.5 mm, 9.69 g, 7 h). Rome mint, Struck A.D. 77-78. Rare. CAESAR AVG F DOMITIANVS COS V, laureate head right / S-C, Domitian riding horse left, hand raised and holding scepter. RIC 1053 var (Spes) (Vespasian); BMCRE 745 var (Vespasian). Fine, porous. 

This reverse type is not listed for the year "COS V" in either RIC or BMC.The reverse type refers to the "magnificently adorned white horse" Domitian rode in the triumphal parade celebrating the Judaea Capta. (Seutonius, Life of Domitian)