I have to admit that as a newcomer to the region I'm grateful to Lowe's for posting this sign. However ambiguous it may appear, it clarifies some confusion regarding Arizona shade, that blessed equivalent of full sun in more northerly latitudes. And obviously not even quite the same as California shade.
This point was further emphasized in Gardening in the Desert by Mary F. Irish, formerly with the Desert Botanical Gardens. She states concisely that "Shade helps everything." (An excellent book, which I picked up recently from our local Friends of the Library. I am an unembarrassed second-hand book lover.)
However, these little signs also demonstrate one of the difficulties of plant-buying when the plants are trucked in from a considerably different growing zone. I try to do my own research before heading to the garden centre, and I often use my trusty smartphone to doublecheck information on plant tags. And there is always common sense. But there is no replacement for watching plants grow in a given environment.
So I buy the plants and watch. After all, I am very new to this!