Yeah, its a little picture of a AA style battery that is in the upper right of the manual. It has, "backup memory" in kana written inside the battery. This is the same feature that will give the ability to save to HuCards if they are being played with a Turbo Booster Plus, Save-kun, or any CD system. I haven't tested that, but I'm pretty sure its the case. Memory Base 128 games have a different logo.
I don't see a list of these type of HuCards on the PC Engine Maniax FAQ. The games I have on these types of HuCards are Formation Soccer '94, and...hmmm...that's it. Mostly its for sports games, but I've seen it on other kinds of stuff.