I’m going to throw it out there – what is the point of non-required fields? Obviously the company that you’re submitting information to doesn’t really need whatever the field is asking for, so why ask for it?
The only time I can see it being necessary is for extra address information – you know, second floor, apartment number, etc. I can’t think of any other time an optional field would be useful (leave a comment if you have ideas).
So marking required fields should really not be necessary either. Best practices suggest that if most of your fields are required, you should instead mark the fields that are optional.
However, if you feel the need to mark your required fields, you really only need one asterisk. But that’s not good enough for H&M. On a contest they ran recently, they decided that you might not notice a field was required unless they used two asterisks: