These days, badges with a makers mark on the slider are sold with a premium. Great care should be taken with maker marked badges in particular ones that are marked JR Gaunt.
A fake Gaunt maker mark will be as in the top example, J.R. GAUNT.LONDON and will be 15mm long and just over 1mm high.
Genuine Gaunt maker marks J.R. GAUNT.LONDON can also be found (although uncommon) but these are only 11mm long and just under 1mm high as in the middle example. Genuine J.R. GAUNT LONDON marks can also be found without the dot after the letter T and these too are also 11mm long and just under 1mm high as in the lower example.
Genuine Gaunt badges (marked or not) will always have an oblong sweat hole behind the Coronet and a round sweat hole behind the Rose.
Gaunt fakes and copies do not have sweat holes.