This is a gorgeous little piece of glass and, yes! That "L" says it all.
The faint letters to the right of the script "L" should say "STERLING" in upper case.
The glass is by top Bohemian/Austrian maker Loetz, though the script "L", interestingly, does not stand for "Loetz", it's the mark of the La Pierre Manufacturing Co. New York, so the glass was made in Europe and the silver overlay was done in America.
Silver overlay on glass is an extremely skillful and technical feat to master and only America, Japan and Germany have been able to make a commercial success of it.
The Germans and the Americans invented the process almost simultaneously and in Europe it was one particular German, Friedrich Deusch, who took out the first patents. He came up with a method of coating silver in intricate patterns onto glass (or porcelain) in a three step process that permanently fused it to the surface by first etching with hydrofluoric acid and, second, painting on a flux of solvent and powdered silver and third, building up a thick layer using electrolysis.
It was around 1905 when the first silver overlay in was done in America (by the Electrolytic Art Metal Company [EAMCO] of Trenton, New Jersey) so this is the oldest your vase could be, however, it was not until the 'teens and 1920s that companies like La Pierre began to specialize in silver overlay, so I would say this is the date of your piece.
It's the height of Art Nouveau elegance, with its flowing orchid blossoms, or are they irises? Hard to tell.
These are very desirable little gems of art glass and silver. This somewhat battered but similar example sold on line for $500.
I would give yours an eBay/auction value in the range of $600 - $900.
Full retail/replacement/insurance value: $1800.
Hope that makes your evening a little more iridescent! Or even "Loetz more iridescent", sorry couldn't resist!