This small white Starbucks espresso mug was tested with an XRF instrument in June of 2014 and was negative for lead (Pb), mercury (Hg), cadmium (Cd) and arsenic (As.) The year of manufacture of this piece is unknown, but it was fairly new at the time it was tested (sorry I did not think to take a picture of the bottom mark when I tested it!)
Given the unpredictability of Starbucks mugs at this point (July of 2018) my general advice is to avoid using them until the come back to the fold of branding solely lead-free mugs with their name.
The other items in this photo (the wooden robot toy and the wooden block) are also lead free!
As always, Thank you for reading.
Please let me know if you have any questions.