anyone know what they mean? I have them next to my happiness and defense values.

It means you don't have enough of that, I noticed it during the tutorial quests when I wasn't finished adding food, it had one beside food in my pip boy.

Reminder to boost your settlements accordingly.

To reduce raids on setllements, you need defense value = http://forums.bethsoft.com/topic/1546414-warning-triangles-in-pip-boy-workshop-screen-next-to-defense/food + water output of settlement. If lower, you get that warning icon

Happiness, you need minimum settlement stuff like enough beds for every population, enough water, etc. warning icon is reminder you need to boost your settlement accordingly