Hi,
Confusingly, Castello is a district of Venice where some glass is produced, but is not on the island of Murano.
More likely given the design is that this is from Castello Glass who are a dutch company (Castello Glas BV) who have glass made for them on Murano. However, I can't definitively confirm the maker or mark as the only Italian glass I have handled that was labelled Castello had beer of the same name in it. :cheers: