I was told that French is the easiest language to learn as an American english speaker, but I was a?

In my opinion french isn't easy at all. There are lots of irregular verbs. It is much easier to learn spanish. I don't know about sign language though, but I would think that it is easier than french.

I speak 9 languages and, except Turkish and Arabic, French has taken the most effort because one word blends into the other, so comprehension is extremely difficult until you practise. You'll love French if you do take on the challenge, but sign language (which I do not know) would likely be easier, especially given the ease of telling one gesture from another as opposed to one French word from another (they blend, giving it its famously unguteral tone).
I wish you luck with whichever you choose.