Didn't see the thread several threads behind this one that says the same thing. Sorry Chaosrising. I have added additional information though.
I have been thinking about how Isshin and Uryuu's father know each other and whether they will make an appearance in the pendulum chapters (probably not).
Isshin is a noble (particularly of the Shiba clan) because:
1.) He has a white scarf thing draped over his left shoulder. Byakuya has a white scarf. Yoruichi has a white scarf when she fights Soifon. The white scarf seems to be the mark of Nobility.
2.) Shiba clan is disbanded and so is Isshin's status as a Shinigami.
3.) Kukaku and Ganju have the hook-up with Urahara who obviously is close with Isshin.
4.) Ichigo looks EXACTLY like Shiba Kaien. It is even mentioned to Rukia by one of the characters (I forget which one).
5.) Isshin wears his sword Tachi-style (edge facing down).
From wikipedia, "In later Japanese feudal history, during the Sengoku and Edo periods, certain high-ranking warriors of what became the ruling class would wear their sword tachi-style (edge-downward), rather than with the saya (scabbard) thrust through the belt with the edge upward."
6.) Ichigo's hollow refers to him as "King." I know this is a stretch and probably has nothing to do with it but you never know.