Just how successful was DC Comics' highly publicized Blackest Night ring promotion? That's what Marvel would like to know.

In an apparent attempt to find out, the publisher is offering direct-market retailers "an extremely rare" variant in exchange for covers from unsold copies of six titles linked to the DC promotion.

According to a press release sent this afternoon, for every 50 stripped covers Marvel receives by Feb. 16, retailers will qualify to receive one free Siege #3 Deadpool Variant.

The specified titles -- Adventure Comics #4, Booster Gold#26, Doom Patrol #4, Justice League of America #39, Outsiders #24 and R.E.B.E.L.S. #10 -- received significant sales boosts in November, thanks to a promotional incentive that allowed retailers who ordered a certain number of copies of each book to buy bags of the corresponding color plastic rings. For instance, for every 50 copies of Adventure Comics, retailers could buy two bags of blue rings, and for every 25 copies of Outsiders, they could buy two bags of violet rings.

In the case of a low-selling title like Booster Gold, the promotion meant an order increase of more than 35,000 copies over the previous issue. Critics at the time questioned how many of those would end up in the dollar bin. But a good number of fans and eBay sellers didn't care -- they were just happy to collect the plastic rings in Pokemon-like fashion.

The Marvel release notes that the offer isn't a Diamond-affiliated promotion, and that the distributor shouldn't be contacted. Instead, Marvel will get in touch with retailers once the publisher receives their submissions.