The best way to tell I think would be if you had some iodine hanging around and could make up a small batch of tank water with the appropriate dosage in a white container. Within a minute or two of submerging the coral, if you shake it around you would see worms coming off and settling to the bottom. And if you don't see any then you can keep an eye out I guess. A couple of minutes shouldn't really stress the coral too much. Full on iodine dips are 15 minutes and doing those too often quickly leads to unhappy acros. Which I guess is when you spring for CoralRx.
If you do ultimately find that you have them, there have been one or two excellent threads on here recently about dealing with them.