Yes Ahremck, your explanation does sound very plausible. From studying the pwt it does not have any digits.
The photograph does do the actual signature justice however, I will try the tulip idea and also try under a lit glass table. I also tried the advice provided by Kevin's link, perhaps I did not tilt it towards the light correctly.
Ross, I got the weight from an antique fair in Shoreham-By-Sea, Brighton way.