Instead of the dogs welcome sign, you could use the lot traits that attract dogs and their owners and the one that attracts stray dogs. I don't remember what they're called, but they should be easy enough to spot in the lot trait panel. Maybe this what you meant, but I believe there's also a rug that says dogs allowed? I figured you might be referring ro that object.
If you do have strays on the lot, add a vet table or the vending machine because strays are almost always sick.
There are some deco objects like the pet food bags and the pet treats jars that you could use to at least make it look like a sample/sales display of pet food.
Maybe your active sim can sell hand knitted pet clothing? I don't know if the can be put on the sales table though. And they will just look like packages. But it's worth a try. You'll need cottage living and nifty knitting though.