What I had done sometimes when writing slashed zero by a pencil and needed the disambiguation (which is not that common in my writing but it does happen sometimes that it will be important), is for the slash the other way for zero, to avoid being confused with slashed O or the symbol for empty sets. Atkinson Hyperlegible font (mentioned in another comment) also works that way, too; the slash for zero is the other way than the slashed O in languages that use that.