His father, born at Saint Helier, Jersey, was then working as Tally Clerk at Queen Street wharf, progressing to prominence on the waterfront as the representative of various overseas shipping companies.

There, without any definite thoughts on design at that point, he studied under the British industrial artist, Harry Wallace, who'd emigrated from England to take up appointment as an instructor at the college in 1904.

[3] After Wilson & Horton, Sinel freelanced in Wellington and Christchurch, then upon returning to Auckland, established a "commercial art and design" practice in Shortland Street.

[3] Sinel appears to have left Auckland on the SS Maheno for Sydney, Australia, in January 1914,[28] where he took to a life of subsistence as a sheep shearer, harvest-hand and rabbitter.

[1] Back in New Zealand and Australia, Sinel worked as an art director and commercial artist mostly on campaigns promoting American products[1] until, on 24 August 1918, he shipped out of Sydney on RMS Niagara for Vancouver, touched at Seattle and, amidst the Spanish influenza pandemic and its precautions, entered the United States at San Francisco.

[1] Harold von Schmidt took him on staff at the advertising firm of Foster & Kleiser, creating posters and billboard advertising then booming to fill any vacant space in town, and working alongside the notable artists and designers von Schmidt, Maynard Dixon, Maurice Del Mue, Roi Partridge, Charles Stafford Duncan, Judson Starr and Otis Shepard.

At some point, Sinel, along with Del Mue, took time-out to explore the Sierra Nevada mountains, where he built a log cabin at Susie Lake, then, as winter closed in, returned to San Francisco and several job offers.

[36] Returned to San Francisco he was employed on lettering by the advertising agency H. K. McCann Company,[37] taught design and lettering at the California School of Arts and Crafts for Frederick Meyer in 1921–1922,[34] produced book illustrations and designs for the San Francisco publishers Edwin and Robert Grabhorn, the Grabhorn Press, established in 1920,[38][39] then, for some five weeks, was an art director for Charles Corbett Ronalds, who'd established Ronalds Press and Advertising Agency Limited in Montreal, Canada, in 1918–19.