Possible Clues:

• More valuable, as coins
• It's comparatively unusual so to get this less well done
• More enticing to a philatelist, say
• Relatively red
• Less common, more like an underdone steak
• Like $2 bills, compared to most bills
• Thinner artist runs about inside
• More unusually more underdone
• Pinker or harder to find
• Less encountered