Steps

1. Create measurement attribute e.g. Weight and select base unit e.g. kilogram and sign e.g. +-

1. Assign this attribute to a Product type
2. Create a new product of this type
3. This measurement attribute is displayed but not with this predefined unit (but with unit placed first in the list) and sign is missing

Result:

each time I have to switch the unit when I create products of this type.