Fast reference without an index?

A question to the hackers:

Is there a way, and if I'm being stupid please tell me, to use something
like a row ID to reference a row in a PostgreSQL database? Allowing the
database to find a specific row without using an index?

I mean, an index has to return something like a row ID for the database to
find the row, right? Granted it has to find the version with the right
transaction ID, but still, you get the idea. In the old days of ISAM
stuff, it would just be the offset into the file.

In my text search system, rather than create an additional indexed column
for row ID, wouldn't it  be more efficient if I could use PostgreSQL's
data for this? This would greatly improve the performance of FTSS as it
would eliminate the extra index operation per row returned.