It's from this set, which is actually a 20 card set, not 18. I don't recall who the last 2 cards are.
http://www.tradingcarddb.com/ViewAllSet.cfm/sid/95180/1990-Living-Legends-Blue-(Unlicensed)?PageIndex=1#6680538
I have tried for years to figure out where some of these came from. There are also orange, and silver border sets. None are really hard to come by except for the yellow. Probably someone made these in their garage, or when no one was looking at one of the real card companies. For a while I thought some of these may have come from a magazine, in a sheet form. But after searching for some time, never found anything on that.
We've had this discussion here before, but some will tell you these are worthless and should be destroyed. I don't agree, they are not worth much. Not having that MLB stamp hurts it, and is part of its appeal. A cheap "knock-off", or "bootleg" is all it is.
I resisted them for many years, until I noticed some are quite nice, and sometimes have photos you won't find anywhere else.
"I believe there ought to be a constitutional amendment outlawing Astroturf and the designated hitter." - Crash Davis