The opening bars of some songs are so strong that you find yourself hooked, the moment you hear them. Rhythm and blues, when it was rhythm and blues had many classic opening bars.
And what about that opening guitar riff by Mark Knopfler on Money For Nothing?
Sometimes it's not the bass line (although that is often most memorable) but just the "sound." Recently, I put together a CD of favorite stuff of mine and refreshed my memory on There She Goes, but the Las. I remember the first time I heard that record. I was shopping an a Farm And Fleet store in Southern Wisconsin and it came on over the loudspeakers. I knew I had to have the record before it was half way through the song.
There are some jazz songs that come to mind, too. The opening bars of Mercy, Mercy, Mercy by Cannoball Adderly come to mind.
At the moment, no folk recordings do, although the chunka-chunka sound of Mother Maybelle's guitar line immediately identifies a song as a Carter Family song. But, the opening bars aren't distinctive to a particular song. Almost all Carter Family recordings start out with the same introduction and rhythm (maybe Hello Stranger) would be an exception.