This depends on the type of safety signs you will be using in your workplace. For instance, TRADESAFE aluminum safety signs have 1/5" drilling holes in each corner which you could screw to the wall (screws not included). Make sure to place your safety signs on a strategic part of the wall, where they can be seen up close, at a distance, and from different angles.
As for TRADESAFE floor sticker safety signs, all you have to do is to peel off the back to reveal a strong acrylic adhesive that will stick very securely on most surfaces as long as they have been cleaned and dusted off. Ideally, floor signs should be placed on the floor but you can choose to stick them on walls as long as these signs serve their purpose.