Firemen will probably be new to your building, therefore to save their time, signpost the location of this and all other fire protection equipment. Conveniently, the sign will even glow in the dark when there is a lack of light, as it is Jalite AAA photoluminescent. 

Do the responsible thing and signpost the sprinkler valve clearly for all to see. Fixing requires anything as simple as sticky pads, 'No-nails' type adhesive or double-sided tape.