Yes, there is a way to test unmarked diodes.
A curve tracer, or factory test equipment.
An ohmmeter will tell you if its germanium or silicon though.
OTT - Well without a curve tracer I know of no real way to test diode voltage ratings UNLESS they are zeners. (See my posting on testing them with an eye type cap. checker on this site).
Silicon stacks like that were used for HT rectifiers and focus diodes --s u p p o s e d l y --can be given a go-no go test using a light bulb for current limiting and a HV source. Personally, I have my doubts on that method, although a TV repair journal did tout it. Typically TV type HT rectifiers are good for about 2 MA., IIRC. A bulb would use a lot more current.
If I could remember where I saw the circuit, I'd post it. I do not recommend trying that method though.
Signal diodes were either glass or metal- (Typically WE)- encapsulated. There might have been some top hat types too, but in the beginning, I think they used whatever case they could. (I do have some 1N34 & 1N60 types in ceramic, as well as 1N23,A ones too. Huge casings compared to todays glass casings.)
Now the 1N4007 can replace the huge ceramic and selenium rectifiers they used in TV sets power supplies "Way back when". (See my article on full length leads and current de-rating for diodes posted on this site too).