I was at a wake for an old friend a few days ago. One of his sons is a member of a well known organization of motorcycle enthusiasts. There were a few of his fellow members at the wake, wearing the typical outerwear unique to this organization.
There were ball peen hammer patches on the jackets. One of them was wearing a tee shirt with crossed ball peen hammers on it.
What is up with the hammers?
First off, as a motorcyclist myself, I don’t like the use of “well known organization of motorcycle enthusiasts” there. Let’s just go ahead and say it. If we are talking about the same group (the Hells Angels), I think it would be more accurate to say " a gang of outlaws who happen to ride motorcycles".
But, to the core of your question, apparently carrying a hammer is a well known way to skirt laws against concealing a deadly weapon. A hammer can be a useful tool, so it can’t be said that they are carrying it just to bust some skulls. Of course that IS why they carry them, but the fact that it is a tool that you could somewhat reasonably use to repair your bike with, they get away with carrying them.
That is exactly the group I am talking about. Thanks for the answer. It makes some sense now.
Not sure of the veracity of this as a cite, but it’s what I found:
keep in mind that the term “outlaw motorcycle club” came from clubs who didn’t seek sanctioning from the American Motorcycle Association (AMA,) not that they were necessarily involved in criminal activity.
Bolding mine.
A distinction that doesn’t apply to the subject of the OP, The Hell’s Angels.
Aside from the obvious use as a weapon in a fight, I’ve also heard stories of outlaw bikers commonly using ball-peen hammers for a different purpose – knocking off the mirrors of cars whose owners have pissed them off on the roadways. After all, you’ve got it in an easy-to-grab spot on your bike…
A nitpick, but a fascinating one, at least to me. It is NOT Hell’s Angels. It is Hells Angels. No apostrophe. Their website plainly points out that this is intentional.
[QUOTE=Hells Angels website FAQ]
Missing apostrophe in Hells Angels? Yes, we know that there is an apostrophe missing but it is you who miss it. We don’t.
[/QUOTE]
A patrolman from the Sturgis Police Department said:
The first I’d ever heard of a ball peen hammer being the weapon of choice for The Hells Angels was from the documentary Outlaw Chronicles hosted by a former Hells Angels president-turned-informant (and TV personality I guess) named George Christie. He claimed that it was preferred because the nearly-symmetrical head of that kind of hammer allows you to quickly pull it out and hit someone with it without worrying about whether you’re holding it the right way (unlike, say, a claw hammer). It’s also lightweight and fits in your belt securely. Seems plausible to me.
Funny old world, in’t it?
Screwdrivers and heavy flashlights are also used for this purpose.
Didn’t they have an official HD part number in the AMF-Voit days?
This is one for the experts I fear. I recall that Ed McBain in one of the 87th Precinct books had young detective Bert Kling thoughtfully explain to his girlfriend exactly why a claw hammer is the perfect weapon. For a woman.
Follow-up question: what motorcycle repair, if any, specifically calls for a ball peen hammer?
Go up to a Hells Angel and ask them. 
I guess I’ll go look it up, if I remember, but…what the hell does “peen” mean?
Does everyone in this thread know but me?
It means “the opposite face of a hammer,” i.e. the non-striking side of the head.
Back when rivets were a more common form of fastener, you would stick the rivet through a hole and flatten the end of the shank. This flattening action is called peening. The tool used to peen a rivet (if you’re doing it by hand - not a jackhammer like pneumatic peener) is a ball peen hammer.
http://www.forth-armoury.com/research/peen_rivets/how_to_peen_a_rivet.htm
Missed the edit, but here’s a graphic that shows the steps:
I’ve used them on cars (not motorcycles) to loosen rusted brake rotors. You spray the bolt that holds the rotor in place with some rust penetrator, hit it with the ball peen hammer, and it tends to come loose.