Although there are plenty of photos of the Jackson 5 signing autographs for fans, early Jackson 5 autographs are fairly rare. If that's what you're looking for, don't be fooled by the signed Jackson 5 photographs you see on eBay. While the autographs themselves may be authentic, most of these were signed by the group members when they were much, much older.
Since the Jackson brothers were still quite young when they first started signing autographs, early ones are fairly easy to distinguish from later ones. Here's a good set from 1972 that even includes Randy and Joe. You can see that Michael's signature is still childish, although he is already beginning to develop the characteristic M and big looping L that he would carry into adulthood. As an added flourish, he's even included a J5 heart to the bottom of his signature, as did Jermaine. (It's hard to tell who is imitating whom here -- although Jermaine did go on in later years to add a smiley face to the inside of his initial J. Just sayin') This particular autograph was acquired by a fan on-board an airplane, so the Jacksons were a captive audience with plenty of time to write with care and flourish. (Poor Johnny and Ronnie must have been sitting in coach.)