Above is a poster produced for Swiss chocolate makers, F-L Cailler in 1934 by Swiss artist Karl Bickel (1886-1982). Very fine it is too, crisp in design and execution; not at all dated, no lingering air of nostalgia. Look at the signature he employed (enlarged in box), formed from a reversed letter K and a B and compare with the logos below for the celebrated Bluetooth specification protocol. Not a lot of difference to be seen. There is more about this logo and the dire consequences of misuse at Wikipedia.