I’m not sure what you are doing with the data that you need the sign separate.
If that’s the case a quick fix is run 2 queries.
First extracting negative temps and define a field sign and set it to ‘ – ‘.
Then extract positive temps and define a field sign and set it to ‘ + ‘.
Then add these results to the ouput file from the first.
Just a thought..
If this is for long term use a program would be the best solution