29 CFR 1910.22 (b) states:  Aisles and passageways.  (1) Where mechanical handling equipment is used, sufficient safe clearances shall be allowed for aisles, at loading docks, through doorways and wherever turns of passage must me made.  Aisle and passageways shall be kept clean and in good repair, with no obstruction across or in aisles that could create a hazard.  (2) Permanent aisles and passageways shall be appropriately marked.

Use Mighty Line aisle marking tape, angles, T's and dots to appropriately mark permanent aisles.  Click on "Catalog" for details and pricing.