According to McGuinn-&-Bazelon's extensive book on dating button-backmarks, Pettibone Mfg. Co. was a dealer in "military, theatrical, and [fraternal] regalia" from the mid-1870s into the 1970s. (But note, Pettibone did not actually manufacture any buttons.)
I myself have seen a great many religious/fraternal regalia items, including swords, buckles, buttons, hats marked Pettibone Mfg. Co. from the latter 1800s through the first half of the 20th Century. I believe your buckle is a religious/fraternal organization's buckle, because the shield on it appears to show a lamb carrying a long cross. (In such depictions, the lamb represents the Lamb Of God, Christ Jesus.)