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I managed to get hold of a ball with an actual signature on it.
Literal
Genuine-autograph signature-contained ball [object-を] hand-[in-に入れる] did.
A compound-heavy collector's-brag sentence. 直筆 (じきひつ) is 'one's own handwriting,' 'written by the person themselves' — important for autograph and manuscript collecting. 直筆サイン = 'a signature written in the person's own hand.' ~入り ('containing X,' 'with X inside') is a productive suffix: ミルク入りコーヒー (coffee with milk), 具入りおにぎり (onigiri with filling), サイン入り (signed). 手に入れる is an idiom literally 'put into hand,' meaning 'get hold of,' 'acquire.' ~ことができた ('was able to X') marks it as an achievement. The whole sentence is the language of successful hunting for collectibles.