Never heard of it before, googling the phrase it seems it is illustrated by graphs. When you strain something it is usually filtered Stain is something that happens when a liquid substance is spilled on a surface that absorbs it leaving a mark.

Are you talking about straining your eyes when you try to read something small? We refer to that as 'reading the fine print.'

I've never heard the term before. I have two theories. 1) It is a very strange mis-transcription, perhaps a computer spelling checker error, of the term "screen printed." 2) Based on a web search, I wonder if it is, specifically, reference to a Colorado firm named "Strain Printed?" It makes clothing designs that features the names of strains (varieties) of cannabis.