Actually, as Joseph Green, wrote offlist there ARE instances where the apostrophe is required to denote a plural!!!! read on:
>"Finally, use the apostrophe when adding a grammatical ending to a number,
>letter,
>sign, or abbreviation: 1920's; his 3's look like 8's; p's and q's; he got
>four A's; too many
>of's and and's; she X'd each box; K.O.'d in the first round."
So if cisco is an abbreviation, "there are many cisco's" and "cisco's profits are high" are both correct, though in one case the apos. mean plural and in the other, it means possessive.
I don't think this was my students' problem, but at least now I know.
Joanna