Thats going to be a gorgeous sign. I've never used purple heart. I've heard it may bleed so, I'd use a water based spray finish. Water based dries pretty fast. Spraying would eliminate any transfer of the color you might get from a wipe on or brush application.
I wouldn't add a border. And, any routered profile would be as to your tastes.
'The true soldier fights not because he hates what is in front of him, but because he loves what is behind him.' G. K. Chesterton
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