Unless grinding is specified, whether to grind or not to grind is left to the contractor's discretion.
As to the discussion regarding the term “flush”, some codes define what flush is. AWS D1.1 is an example of a code that does address what “flush” is.
Al
Since a weld is only defined as complete when it is at least flush, it is not a matter of allowing grinding. If the contractor wishes to waste time grinding down perfectly good welds, they are free to do so. Most codes establish maximum re-enforcement of welds as well as flush standards which will also set maximum amounts the base material can be 'thinned'.
Yes, they really do have the option to grind or leave as welded. Why they would want to waste time grinding would cause me to examine the weld very closely. WHAT ARE THEY HIDING??
Having the symbol makes it mandatory to be reasonably flush. Having the symbol WITH a 'G' over it makes it mandatory to GRIND it as flush as possible. Clause 5 describes flush. I will let you find the complete text.