How to create custom ability that adds +2 to your next attack roll automatically?

Hi! I'm played a ranger in a game and I get a damage bonus when fighting against favoured enemies. I was wondering if it was possible to create an ability down in the macro bar that when pressed, automatically adds +2 damage to the next attack roll? I'm very new to all this stuff, and I've been looking at the wiki to help, however there's a lot I don't understand and am still learning! (:

Unless your game has API enabled, you'd probably want to use a global damage modifier for that. You have two choice - either fill in the damage as a flat 2 and remember to flick the checkbox on and off depending on your target, or throw a Query in there and leave it on most of the time:

?{Favored Enemy?|No,0|Yes,2}

That will pop up every attack and could get annoying - though you can still switch it off.

Bear in mind that this can only be done if the sheet supports it (with something like the global damage modifier Oosh mentions), or you modify every single attack macro you use to make rolls and add a query like the one Oosh suggests.

Ah yeah, I was assuming 5e Revised Ranger from your description. If you're not using the 5e sheet that link is not much good.