I just clicked through 20 scripts from my disk with 460 script pdfs - and none had bold sluglines. Mostly number scripts like 48 HOURS and 101 DALAMTIONS.
Don't bold your sluglines. It's not standard format.
If you send your script out like that, it'll scream amateur. If it's just for your own use or you're shooting the film, then do whatever you want! It's your script.