A suggestion, rather than a pesonal recomendation:
http://www.dive-logs.com/products.jsp?ProductCategory=15&Referrer=Google4

For torches, cameras etc, write your name and details on batteries or
labels inside the device as well as outside.

CD pens are usually pretty good, but try to pick a place that isn't going to
get rubbed.
The markings on my Quattros have survived pool, sea and fresh water over the
last three years.

HTH

Deep.

   http://tinyurl.com/y6mzpc

 100s of dives, and still going strong.

 Note that the given price is -per marker-.

 I keep white and yellow in the kit.

I have used a Pentel Correction Pen (a branded correction fluid, aka
Tipp-Ex, aka Wite-out, aka Liquid Papar) with great success.

We usually mark club & rental BC's on the outside of the pockets, and I
mark personal stuff inside the pockets, which is less unsightly and
seems to last longer. It also works well on the inside or outside of
wetsuits, gloves, booties, and neoprene mask straps.

Some people use it on fins, too.

Club & rental DV's (1st and 2nd stages & cylinder valves are engraved,
and we spray the club name on two sides of the cylinders with fire
engine red in 20cm high letters which is visible even when the cylinder
has a net on.

We have recovered lots of stolen gear from dive shops, cylinder testing
stations and all manners of pawn shops and second hand sports gear
shops with great success.

Taking down serial numbers also helps a fat whack and so does taking
digital photos of all your gear!

HTH

rgds
monty

Thank you everyone for your excellent help and advice.

I suspect I will use a 3 prong approach and use the paint marker pens
the tags and etch serial numbers into the stuff that can be etched :)

Jon