Do you break the continuity of play time to go look up the sign? (No way!) Do you give up on taking advantage of this Signing Smart Opportunity? and just wait for the next one? (You could, but you don't have to!)
Think about it this way...when you're telling someone a story about your day and you can't think of the word you want to use, what do you do? You probably substitute a different word or describe the object you're talking about. We actually do that pretty naturally in our native language.
Here's an example: Mr. I. is 3. On a recent trip to a local zoo, he had his first carousel ride and LOVED the experience. The next time we were there, he wanted to ride again, but just could not remember what it was called. The conversation went something like this: