To help students get used to recognizing the whole and half rests upside down, hold up a whole rest card upside and ask them, "What is this?" They will answer, "A whole rest".
Turn the card upside down and ask the question again. I've found they are most likely to answer, "a half rest". I usually don't respond right away, an unspoken way to encourage them to think about it. In a short time someone will answer, "Oh, I know! It's a whole rest upside down."
Someone will answer, "Because of Freddie." I'll see recognition cross all their faces and I'm glad to know they are thinking. "And dogs don't fly." (laughter)
It helps to illustrate the same point using an A alphabet card. "It's an A no matter how I turn it, right?"
The students will soon be fast at recognizing the whole and half rests even if they are upside down. Think about it - if you can recognize a whole rest upside down it means you really know it.
It's useful to point out how the guide cards can help them when they need them.