Here we come to one "Diamond" in every collection.
Nice or not nice, it is one classic issue from 1919 year, overprint on Austro-Hungarian stamp (Michel number 205 II), catalog Michel have it by number 56 IIb, 3 Kr lilarot (lilac red),
overprint "Posta Ceskoslovenska 1919" in black color, and Scott have it under number B19a.
Examining Scott and Michel catalog, also Specialized Czechoslovakia catalog, I see that this issue is not summarized in "set" like we know to name some issue of x, y stamp in issue - that mean, this overprinted stamp come to the use "as situation required" but here we have too much to study, which is not my intention at present - I'm not so big specialist in this field.
Now, why I think that it is worth to have?
First, it is early period of country, after that one more reason is overprint alone, next come that this specific stamp is not in "basic" set - mean, that "basic set" value of 3 Kr come in brown-carmine color, and here shown come in claret. Scott mention this "variety" (number B19a), which is actually not variety, but regular color of original Austro-Hungarian set.
I just purchased this one lot of 4 stamp, where between four, one is exactly mentioned number, in VF, LH condition, og.
What decided that I go after it was, rarity of this issue, and because it (specific stamp) is signed on back, which actually is some kind of certificate about same. I don't have wish to track and buy one sample with certificate, also because it will be so costly and also because not many of this stamp are know. Signature on back actually give me some kind of secure sleep, when is talking about forgery - but, without certificate it still have one level of chance that it can be "bad".
I also read little about this stamp in "Specialized Guide for Czechoslovakian Stamp" which say that color is correct and also dimension is correct, actually existed "small" (25x30 mm) and "big" (25.7x29 mm) dimension, which just confirmed that I have right stamp.
What say catalog value?
Michel 2000.00 euro, Scott 2750.00 $ and "Guide" (don't have prices - but "points") marked it 2R (mean: 201 to 400 know discovered). If I know that my sample is in VF, LH condition, that will reduce level to one fair market price of around 60-70% of Michel catalog.
Want it, have it? Keep for it, and if it is in Your collection - put it on the bottom of box, as dark side as can be - it is really one valued stamp!