From a recent NE Texas Estate sale:  Vintage Blue Letter O for Ox baby toy . 
No makers mark or other identifying mark, probably an old dime store type bath toy.  Softer plastic (not hard plastic, not rubbery).  I have several other letters from the same set in my store- but not the whole alphabet.  Very good- excellent played with condition- no cracks or other damage found.  Would be cute for decorating or for topping a gift for someone with the initial O. 
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