Puffer, do you have a popup ad blocker in effect? If you do, you need to add www.cryptograms.org
to your list of exceptions to the ad blocker. In my experience, the "Subscribe" ad came up only when I was blocking the popup ads. When I added this site to my exceptions list, thus allowing the ads to appear, the "Subscribe" ads stopped appearing with every window.
The site is set up so that if you can't or don't want to pay for a subscription, you will instead have to allow ads to load onto every page. Basically, you can't play for free -- you pay either with money or with your willingness to see ads.