"The absence of proof is not proof of absence." - William Cowper, poet
According to the Oxford dictionary, the definition of an "angel" is "a spiritual being believed to act as an attendant, agent, or messenger of God, conventionally represented in human form with wings and a long robe". We always think of an angel as someone who has wings like that of a dove, with either a sword or a harp or even a bow. But there's some stories implying that not all angels are like the picture below. In fact, some of them are literally in their human forms, living with us without noticing them.
To me, one thing is for sure - angels are God's workers. Maybe they're just waiting on us to finally notice them. Maybe they've been watching you closely than you are aware of, just waiting for your 'go' signal...