This is actually sterling silver and not gold. The stamped hallmarks are British sterling marks. The lion stands for the UK, the anchor for Birmingham in England. The initials T.K. & F are for the early 20th century firm of Tozer, Kernsley & Fisher. At 5mm length this is a miniature piece.
The estimate is based on actual recent past recorded auction sales of comparables. Retail 'asking prices' can be higher and vary.