Sorry Paul,
I cannot help with this, and certainly this does not appear in my database of more than 4500 items of post-war Czechoslovakian production.
You should be wary of the bird-bath base-well, as this could also apply to glass from VLG Lausitz, Ankerglas, VEB Sachsenglas Ottendorf-Okrilla, and Zabkowice, and thus is a feature of pressed glass production, rather than a clear indication that an item must be Sklo Union.
Regards,
Marcus