New Press on Attack Support Rune?

Press on attack has been changed from increasing ad based on stacks from attacking people to "attacking the same target 3 times deals X true damage and increases damage dealt from all sources by Y% for 6s".

This looks like a support rune, unless all sources means all sources from the one who put this debuff on the target.

Or did i misunderstood and it doesn't put a debuff on the target and just adds a buff to yourself?