There are obviously some distinctive African looks: east Africans especially. Many native Africans you can spot at a distance.
If you are Black American and by that I'm making a broad term that includes non FBAs who were born or spent their lives in America at an early age, its more than 'a look' The way you carry yourself, obviously how you talk.
When I'm outside America, and I approach someone randomly who I think is black American I first look at how they are dressed. We often dressed distinctly different. I also wait to hear the accent. Then I'll say 'You American?' or if I know 100 percent "Hey Fam"
If I get it wrong, I'll play it off and conversate for a second. I've been asked if I was African. The disappointment is noticeable. lol. They (Africans) automatically assume we have zero in common. And I may as well be white. My usual fun answer is 'about 400 years ago'.
Canadian blacks sound like us but without a wee bit of our swag but by and large, I (and other American friends) regard them as fam. To a slightly lesser extent black Brits. They can be cool and have a what's up fam vibe but there are a few times, I've gotten a cold shoulder.
I've been in countries where they are very racist against native Africans but treat black Americans as de facto whites. Sometimes they aren't sure (the non blacks) so they wait to hear the accent. And with that accent comes a certain amount of 'I ain't taking any bullsh*t' vibe as well.
Some Africans will let locals punk them. They will be next in line and mofos will put their sh*t right in front of yours. That's happened to me a few times and it only happens once. I get very black after that. "Yo..what you doin' playah?" They realize I ain't a native African. Most of us have a 'west African' look for obvious reasons. Many of us were enslaved from there. And if its a country where there are very few if any black Americans they assume we are one of them.
What automatically distinguishes me most times is my fake zirconia diamond earring in my left ear. We are almost always the only ones who do that. Not many Africans do. I've heard some Nigerians have but I've yet to see it.
What I've been told that makes us distinctive as well is that we aren't shy about walking into anywhere or walking up to anyone.
PS: I edited this post to add this. One thing for sure is if there is beef that can escalate, we go in the fastest. I'm no thug, no street cat, obviously a 'blerd' (black nerd) but I ain't gonna get disrespected and punked either. We will put hands on folks quicker than any other black folks. No question. I've had to and me and my boys have. They know that about us too.