Range bonus 3. According to RMS, I looked yesterday but I didn't have time to reply to you.
i think it increases bow dmg by like 5%
According to RMS, it's actually +3% long range ATK.
Why not range? Because Archer Skeleton Card has the same code: { bonus bLongAtkRate,10; } (and the description says +10% bow ATK)
And the Bow Thimble has: { bonus bLongAtkRate,3; }