Our cat population is 5 at the moment--3 of ours, one is our daughter's, and the other is our son's. Both of the latter two will depart to their own homes at some point in the not-to-distant future.
Anyway, the sign is a familiar one to anyone who owns cats. We have had pretty good luck with using Purina Sensitive Systems dry cat food, upon our vet's recommendation. The incidents of cat vomit have drastically decreased.
Here are 3 of the 5: