Only for certain subfields:

Dash (-) that precedes a subdivision in an extended 600 subject  
heading is not carried in the MARC record. It may be system generated  
as a display constant associated with the content of subfield $v, $x,  
$y, and $z.

 From http://www.loc.gov/marc/bibliographic/bd600.html

-Tod

On Sep 23, 2009, at 9:09 AM, Jonathan Rochkind wrote:

> Hi all, I'm writing some marc record display code, and I have a  
> question about the 'right' way to display LCSH headings.
>
> LCSH headings are typically displayed with "--" between components.  
> But looking at the MARC, it looks like the "--" punctuation isn't  
> actually in the MARC field. (A rare instance where display  
> punctuation isn't in the marc!).
>
> Is it correct for any LCSH 6xx field (which you know because the 2nd  
> indicator is 0, right?), to add "--" between ALL present subfields  
> on display?   Do I have the right logic there?
>
> Thanks for any advice!
>
> Jonathan