It's a reflection of color coding (with painted rings or dots) being vastly cheaper than printing text proper. Many lower cost European transistors (almost excl

It's a reflection of color coding (with painted rings or dots) being vastly cheaper than printing text proper. Many lower cost European transistors (almost exclusively the TO-92 variety) were marked with colored dots or half-rings. Similarly some film and tantalum capacitors were marked with colored dots as well. Precision or otherwise higher grade (e.g. ceramic wirewounds) components were always usually marked with text.