Why do I see a red and/or black tag with the letter S on the top left side of some of my cards in my collection?

That's the new logo tagging system for iStripper/iStripper XXX

Thanks. What is the significance? How does that improve my experience?

That's the new logo tagging system for iStripper/iStripper XXX[/quote]

It makes it much easier to identify which cards are of which type.
Black are regular cards. The red are designated as XXX and may include toys.