Covered mug with compartment;R&W Wilson;Phila;2Q19C.

Marked twice on bottom R&W.WILSON in rectangle; also the letter P twice incuse. Attached rectangular compartment with 5/8" round hole through side of mug near bottom into compartment, apparently to allow a liquid to flow into the compartment. Domed cover with applied bird finial. Applied decorative bands near the top and the bottom of the body; two rows of molded banding around the mug . Single scroll handle. Height of handle 5-1/2"; of body 4-3/4". Diameter of mouth and base 3-1/8". Weight 10-1/2 troy ounces. The monogram is a script CO on the side of the mug opposite the handle. Mark and overall condition are excellent (a few minor dents). What is this? A lighting device? Help!