Please do not put your infant carseats on the handle bars of shopping carts. Put the carseat in bottom of the cart if you must bring the seat into a store.
I almost saw a baby tragedy while grocery shopping tonight. A mother had her baby and his seat in the above position and another shopper rammed her cart pretty hard because she wasn't paying attention. The carseat was almost knocked off the cart and would have fallen had the cart not been up against a tightly packed clothing rack.