Read on a popular community blacksmith forum that all anvils employ the English Hundred Weight system. 

That sounds alot like bunk. There is alot of information out there and I know it can be wrong.

Steve,

I'm pretty sure you already know that is incorrect.  Many anvils are marked in English hundredweight, but hardly all of them.  I've personally seen some marked in pound weight as well as kilograms.

Someone's been listening to too much Dylan: every anvil must be stoned.

A Little Learning

by Alexander Pope

A little learning is a dangerous thing ;

Drink deep, or taste not the Pierian spring :

There shallow draughts intoxicate the brain,

And drinking largely sobers us again.

Fired at first sight with what the Muse imparts,

In fearless youth we tempt the heights of Arts ;

While from the bounded level of our mind

Short views we take, nor see the lengths behind,

But, more advanced, behold with strange surprise

New distant scenes of endless science rise !

So pleased at first the towering Alps we try,

Mount o’er the vales, and seem to tread the sky ;

The eternal snows appear already past,

And the first clouds and mountains seem the last ;

But those attained, we tremble to survey

The growing labours of the lengthened way ;

The increasing prospect tires our wandering eyes,

Hill peep o’er hills, and Alps on Alps arise !

Well said.

Yup we run into a lot of 1 book wonders and nowadays 1 show; or 1 youtube video wonders as well.  Blacksmithing is full throng with a multiplicity of "right" ways to do things and is an excellent example of the old saying "If it's crazy and it works---it's not crazy!"

I have around a 410# Trenton that was used in a copper mine by the welding crew and came to me with pretty much no markings, (save the caplet in the bottom), I think I just have to stamp it to suit myself,   hmm troy oz?  Carat weight?  Slugs?