Body Marking...

All depends on the race, as each has their own locations.  Some people bring sharpies to races and just have friends do it.  

I like getting body marked... it's part of the whole race experience for me

What I've normally seen is:
number on each upper arm
number on hand(s)
age on calf

... I've also seen smily faces, words of encouragement, etc. on the other calf

Have your kids volunteer at the body marking point. They always need people there

I tattoo my numbers.  Actually my girlfriend saw some markings on my leg from a triathlon I did and thought I got another tattoo at first.

I don't mind the markings.  Often times I wish they had a slightly more permanent marker because I love to have people ask "What's on your arm".

X2

Dont know how common it is but my tri this past weekend they only marked our calves. Left was category (Elite, Age, Athena, Clyde) and Number and the right was age. I pretty much sweated it off during the race though but that is ok.

I like a challenge.  Plus nothing motivates you to run faster than a pissed off husband with a baseball bat.

As said above, it varies between races. I think the most logical is AG on right calf [because you pass on the left], race numbers on right shoulder [or both, but at least the right], and race numbers on both thighs, between the knee and the tri shorts. This maximizes visibility of the numbers for photos [even in the event that the bib number is folded or otherwise mutilated] and encourages AGers to fight one another for position!

I <3 getting marked.  Gets my mind set for racing!

Elites have both arms marked with their race number (ITU racing anyway) but as far as I know it should go like this
left arm with race number (in case you cheat on the bike and a marshal can easily see it to make a note)
right calf with age (so when you pass someone..or they pass you..it's easy to see how old they are and if you need to step it up a notch as a result)
anything else anywhere else..seems kind of redundant (except for the marital status thing..I usually mark with smiley faces as well)

Numbers need to be on the left arm so the race officials can see them, especially when on the bike.

Also don't understand why, if you pass on the left, you would want the age on the right.

Good point about the marshalls - hadn't thought of that [a lot of the races I do don't have them, which is part of the reason].

Since you pass on the left, the person you're passing will see your age if it's on the right. Since you were obviously behind them, you had a clear view of their right calf and should have been able to observe their age. If not, well, you're passing them anyway so chances are you're just plain faster. Just watch the numbers that pass you and you'll be fine. Not that The Bear gets passed or anything

So when us older folks fly past the youngsters they know it!!!

IMHO, for age groupers, the only mark that matters is the age on the calf (for competitions sake). the number is covered for the swim (wetsuit races), and redundant on the bike and run.

But, I can certainly see how people wear it as a "badge" of sorts.

Can I ask a related question?  If you are athena or clydesdale do they mark that on your calf? Or do they put your age? 

The races I've run with those classifications put that on your calf instead of age.  Some may do both if they have seperate classifications for <=40 and >40 Clydes and Athenas.

LOL....after my very first tri I tried to keep those marks on as long as possible for that very reason!!