OK, I got this ring yesterday to use with my Witch Doctor, who can afford a big downgrade during farming and still function well.
I have switched my Enchantress from the WD over to my Monk and gave her the Leoric's Signet as my Monk is still only paragon 21 and I do not want to take a massive downgrade there.
My question is, the xp for Enchantress still says 4% which is from the other ring I already had.
Is the Leoric Signet working with the Enchantress?
It seems to be but I only tried it out very briefly as it was very late.
ot4ku has it correct. Since you do get the %XP from the signet (you will really only see it in YOUR character's details screen) and the +4 is from the ring with +experience which in my personal opinion is almost useless since the mobs at inferno already give a lot of exp, an additional 5 isn't that much of a boost. Then again, as they say, any boost is still a boost and a few less exp you need to get manually.