hi leo, in the middle ages craftsman would adopt a device or legend that would he would display on every piece of his work to identify that the piece was genuinely his. sort of like a modern trademark. the "Als ich kanne" motto was originally used by a 14th century flemish painter Ian Eyck to identify his work. Several hundred years later william morris used the term but in french, "Si je puis", to identify his products. morris as you may or may not know was a very importamnt figure in english arts and crafts movement. The Morris Chair of american arts and crafts fame gets its name from his company was the original producer of such chairs in the 1860s.
Gustav Stickley is the founder of the american arts and crafts movement. He took many key pieces from the english movement and made them his own. As such he adopted the motto, in modern flemish (dutch as you mentioned) "als ik kan" along with the joiners compass and his signature to identify his work
if you have a local library near you i suggest seeing if they have any books on gustav stickley or the american arts and craft style. my library has several great books along with a dozen or so "how to build" type books with plans. they also have books of old stickley catalogs with pictures of a lot of his work, which is neat to see
also try searching the google for gustav stickley, thats actually how i identified the piece you posted, i just came about it on a google search