Over the years, the "army" pieces in Risk have come in four main styles:
Wooden cubes for a single army, and "oblong pieces" for ten armies, as descried in these 1959 instructions.
Triangular / three-pointed plastic pieces for a single army, and five-pointed stars for ten armies, as featured in instructions from 1969, 1975 and 1990
According to BoardGameGeek and many other sources,
the pieces do belong to Risk.
BoardGameGeek : offer from Game Crafter LLC
The numerals represent armies : I is 1 army, III is 3 armies, V is 5 armies, X is 10 armies.
Rules for Risk 1980, from Hasbro