If the grandmother is paying you to make these, her name could be on it as such: "presented on the birth of Name-of-Baby by So-and-So, and the date." I'd either put my signature with that information, "...and made by my-name" or in another location.
If the grandmother doesn't have a financial investment in the quilts, I think the card she gives with the quilt is enough credit that it's from her. I'd still sign and date the quilt.
I look at my quilts kind of like they are fine art (i have delusions of grandeur! lol) - and artists sign their paintings (on the front, I might add), without consideration to where the painting or whatever will go when it's done.
just my two cents :)