Peter Galison makes much the same claim in Einstein's Clocks, Poincaré's Maps (2003). He goes into more detail about the sorts of patents and the interest in them at the time, including several that dealt with the problem of synchronizing several distant clocks, and notes that Einstein specialized in evaluating such designs.
During the time that Einstein served as a patent inspector, interest in electrically controlled clock systems heightened. ... As electric time transmission grew alongside the telegraph system, coordinated clocks began playing an ever-increasing role in both public and private sites. The number is: 1901, eight patents; 1902, ten; 1903, six; and then in 1904 fourteen patents on electric clocks overcame the hurdles of the patent office. Numerous others, lost to history, no doubt withered under Einstein's and his colleagues' critical gaze.
All these Swiss chronometric conventions–along with a great many others related to them–had to pass through the patent office in Bern and no doubt many of them crossed Einstein's desk. When Einstein began work there as a technical expert, third class, he was chiefly charged with the evaluation of electromagnetic and electromechanical patents. (248–249)
It must be admitted that Galison's evidence is largely circumstantial. However, Galison notes in a footnote that there is not much evidence at all, one way or the other, about what Einstein personally worked on during his time in Bern; and so circumstantial evidence is perhaps the best we can hope for.
Hundreds of relevant patents are listed in the Journal Suisse d'horlogerie during the relevant years (1902–1905). Sadly, the Swiss patent office dutifully destroyed all papers processed by Einstein 18 years after their creation; this was standard procedure on patent opinions, and even Einstein's fame led to no exception. See Fölsing, Einstein (1997), 104.
