At first Frank's questions and words had bounced off in the way most people's did. Sirius was glad to find the Order, but that did not make him the bestest of friends with everyone in it. No indeed, they had to earn his trust the same way Evans did. And she hadn't done it yet. But the way Frank had written...Sirius had picked up on something, which if nothing else seemed to be interest in him and an idea of his abilities. With all that was going to happen, Sirius wasn't going to turn away help from a trained auror and Order member.
So here he was only a couple of days away from returning to Hogwarts, and Sirius had made his way near the cafe. As always, he checked it out first before entering. He didn't want to walk into something unawares. And as he had been invited, that was always a risk. Hell, if Lord Moldypants had people who figured out the journals, it was possible it wasn't Frank at all who had written him.
But with nothing setting anything off in his head just yet, Sirius entered, still wearing his leather jacket. It was well charmed and such to act as some level of protection, which let him take more risks. Recognizing Frank in the line, Sirius came up and joined him. "Afternoon," Sirius greeted him.