Sony is tempting gamers to sign-up to PlayStation Plus by offering a free copy of Rainbow Six Siege. However, the offer is only available to accounts that have never (ever) paid for PlayStation Plus before (even for a month).
The PlayStation Store description for the promotion states:
To be eligible for this offer, you must have a PSN accounts which never had an active PlayStation® Plus membership (14 days trial excluded). Following the purchase of this product, you will receive immediate access to PlayStation Plus benefits such as online multiplayer on other titles, monthly games, and exclusive discounts on PS Store. Your accompanying Rainbow Six Siege game however will activate up to 96 hours after purchase. During this time you will be unable to access the game.
Given that the vast majority of players have had a PlayStation Plus subscription at some point in their life, this promotion won’t be of much use to most gamers.