This can occur if the PSP payment page is loaded into a frame. The payment page must load into a full window for the Padlock/Key to appear.
If you are using frames in SellerDeck Ecommerce, make sure that 'No Frames in Checkout' is checked in 'Design | Design Options'.
If you are using frames in SellerDeck Ecommerce, make sure that 'No Frames in Checkout' is checked in 'Design | Design Options'.