Not very valuable. Ajman is an emirate in the UAE that issues stamps that appeal to collectors rather than just postage. You can find the single stamps, unperforated souvenir sheets and various combinations for very little money. They are also available with CTO's (cancelled to order), perfectly placed postal cancellations done by the issuing postal authority. Here is one ebay listing:
https://www.ebay.com/itm/31358529516...EAAOSwRztg25Yn
Just go to the category 'stamps' under collectibles on ebay and do a general search under Ajman and Ruth or Gehrig to see more. It is better to do the general search as most of these stamps are listed in the subcategory topical stamps > sports rather than the country in the Middle East subcategory.