Mighty Line aisle marking tape from Indoff can be effective when used to designate aisle ends for forklifts.  Unfortunately a large stop sign is not always visible to the forklift operator.  The most effective visual for a forklift driver is on the floor. 

You may use a line to designate the end of an aisle.  I would suggest using red in a 4 inch width.  You might want to alert the forklift operator before the end of the aisle.  I would suggest Mighty Line dots in yellow as a caution color to alert the operator to begin to slow down.

Safety is always the primary concern and whatever we can do to improve traffic safety in the warehouse will pay dividends that far exceed the investment in Mighty Line aisle marking tape.