According to forums, SKL would mean nothing but possibly the makers mark but it's not listed.
Maker's marks are the initials or name of the manufacturing firm or other representative symbol stamped into a gold, silver or platinum item. Also called Trademarks, they often provide the only evidence that a certain piece of jewelry has indeed been manufactured by a certain jewelry maker.
When such marks are present, the jewelry item is said to be "signed" by the maker or manufacturer. In some countries, Italy for instance, official maker's marks are assigned to registered goldsmiths and their use overseen by a body like the Chamber of Commerce.
Sometimes a goldsmith's maker's marks evolve over time and knowing which mark was used when helps the jewelry historian or appraiser accurately dating an item.
In France, historically, the Administration de la Garantie stored copper plates on which maker's marks were stamped (by law) creating a record of the mark. At some point these were all destroyed, leaving us without this valuable historical reference.
The Antique Jewelry University has an extensive Maker's Mark Database to which new marks are added every week.