This is a vintage Girl Guides trefoil enrolment/promise badge.
 
Key Features
Design Symbolism: The trefoil (three-leaf clover) shape represents the three parts of the Girl Guide Promise.
Letters & Symbols: The initials "G G" stand for Girl Guides, and the star cutout at the top leaf symbolises a guiding star. The stem forms a stylised cross or compass needle pointing forward.
Enamel Colour: The pale blue enamel background typically identifies specific sections or senior branches of the historical uniform, most notably the Air Rangers or specialised Extension sections depending on the era and country of origin (such as the UK or Commonwealth nations).
Scroll Design: The blank scroll banner at the base indicates a classic design variant, often dating from the mid-20th century or earlier.
 
 
Manufacturer & Registration Stamping
The Manufacturer: The stamp reads "COLLINS LONDON". This refers to Sir D.G. Collins & Co., a well-known London-based manufacturer that produced official insignia and high-quality enamel uniform badges for the Girl Guides Association. 
The Registered Design Number: The text "REG. No 671782" at the bottom is a United Kingdom Registered Design Number. This specific design pattern was officially registered and patented in 1919. 
 
Badge Age & Uniform Details
While the initial design pattern was established in 1919, Collins produced these variants across the 1920s through the 1950s. Given the combination of the early manufacturing stamps, the textured metal finish, and the traditional elongated pin-back setup, this piece likely dates anywhere from the 1930s to the early 1950s. 
 
The pale blue enamel face seen on the front corresponds with specialized historical uniform branches. Most notably, it matches the early 1920s–1930s UK Extension Guide Section tenderfoot badge (designed for Guides with disabilities or long-term illnesses in hospitals) or early Air Ranger / Sea Ranger divisions before the design criteria was standardized later in the 20th century
 
 
Condition Notes
Your badge retains crisp lettering, a very clean enamel face, and its original long-hinged pin backing on the reverse. Having the intact historical "REGD 671782" stamp clear and readable keeps it at the higher end of its collectible value bracket. 
 
It measures 2cm x 2.1cm.