Two commas stacked vertically, a rare punctuation mark.
98 characters in the Supplemental Punctuation Unicode block.
U+2E00RIGHT ANGLE SUBSTITUTION MARKERU+2E01RIGHT ANGLE DOTTED SUBSTITUTION MARKERU+2E02LEFT SUBSTITUTION BRACKETU+2E03RIGHT SUBSTITUTION BRACKETU+2E04LEFT DOTTED SUBSTITUTION BRACKETU+2E05RIGHT DOTTED SUBSTITUTION BRACKETU+2E06RAISED INTERPOLATION MARKERU+2E07RAISED DOTTED INTERPOLATION MARKERU+2E08DOTTED TRANSPOSITION MARKERU+2E09LEFT TRANSPOSITION BRACKETU+2E0ARIGHT TRANSPOSITION BRACKETU+2E0BRAISED SQUAREU+2E0CLEFT RAISED OMISSION BRACKETU+2E0DRIGHT RAISED OMISSION BRACKETU+2E0EEDITORIAL CORONISU+2E0FPARAGRAPHOSU+2E10FORKED PARAGRAPHOSU+2E11REVERSED FORKED PARAGRAPHOSU+2E12HYPODIASTOLEU+2E13DOTTED OBELOSU+2E14DOWNWARDS ANCORAU+2E15UPWARDS ANCORAU+2E16DOTTED RIGHT-POINTING ANGLEU+2E17DOUBLE OBLIQUE HYPHENU+2E18INVERTED INTERROBANGU+2E19PALM BRANCHU+2E1AHYPHEN WITH DIAERESISU+2E1BTILDE WITH RING ABOVEU+2E1CLEFT LOW PARAPHRASE BRACKETU+2E1DRIGHT LOW PARAPHRASE BRACKETU+2E1ETILDE WITH DOT ABOVEU+2E1FTILDE WITH DOT BELOWU+2E20LEFT VERTICAL BAR WITH QUILLU+2E21RIGHT VERTICAL BAR WITH QUILLU+2E22TOP LEFT HALF BRACKETU+2E23TOP RIGHT HALF BRACKETU+2E24BOTTOM LEFT HALF BRACKETU+2E25BOTTOM RIGHT HALF BRACKETU+2E26LEFT SIDEWAYS U BRACKETU+2E27RIGHT SIDEWAYS U BRACKETU+2E28LEFT DOUBLE PARENTHESISU+2E29RIGHT DOUBLE PARENTHESISU+2E2ATWO DOTS OVER ONE DOT PUNCTUATIONU+2E2BONE DOT OVER TWO DOTS PUNCTUATIONU+2E2CSQUARED FOUR DOT PUNCTUATIONU+2E2DFIVE DOT MARKU+2E2EREVERSED QUESTION MARKU+2E2FVERTICAL TILDEU+2E30RING POINTU+2E31WORD SEPARATOR MIDDLE DOTU+2E32TURNED COMMAU+2E33RAISED DOTU+2E34RAISED COMMAU+2E35TURNED SEMICOLONU+2E36DAGGER WITH LEFT GUARDU+2E37DAGGER WITH RIGHT GUARDU+2E38TURNED DAGGERU+2E39TOP HALF SECTION SIGNU+2E3ATWO-EM DASHU+2E3BTHREE-EM DASHU+2E3CSTENOGRAPHIC FULL STOPU+2E3DVERTICAL SIX DOTSU+2E3EWIGGLY VERTICAL LINEU+2E3FCAPITULUMU+2E40DOUBLE HYPHENU+2E41REVERSED COMMAU+2E42DOUBLE LOW-REVERSED-9 QUOTATION MARKU+2E43DASH WITH LEFT UPTURNU+2E44DOUBLE SUSPENSION MARKU+2E45INVERTED LOW KAVYKAU+2E46INVERTED LOW KAVYKA WITH KAVYKA ABOVEU+2E47LOW KAVYKAU+2E48LOW KAVYKA WITH DOTU+2E49DOUBLE STACKED COMMAU+2E4ADOTTED SOLIDUSU+2E4BTRIPLE DAGGERU+2E4CMEDIEVAL COMMAU+2E4DPARAGRAPHUS MARKU+2E4EPUNCTUS ELEVATUS MARKU+2E4FCORNISH VERSE DIVIDERU+2E50CROSS PATTY WITH RIGHT CROSSBARU+2E51CROSS PATTY WITH LEFT CROSSBARU+2E52TIRONIAN SIGN CAPITAL ETU+2E53MEDIEVAL EXCLAMATION MARKU+2E54MEDIEVAL QUESTION MARKU+2E55LEFT SQUARE BRACKET WITH STROKEU+2E56RIGHT SQUARE BRACKET WITH STROKEU+2E57LEFT SQUARE BRACKET WITH DOUBLE STROKEU+2E58RIGHT SQUARE BRACKET WITH DOUBLE STROKEU+2E59TOP HALF LEFT PARENTHESISU+2E5ATOP HALF RIGHT PARENTHESISU+2E5BBOTTOM HALF LEFT PARENTHESISU+2E5CBOTTOM HALF RIGHT PARENTHESISU+2E5DOBLIQUE HYPHENU+2E60WIGGLY EXCLAMATION MARKU+2E61INVERTED WIGGLY EXCLAMATION MARKU+2E62LEFT PARENTHESIS WITH MIDDLE RINGU+2E63RIGHT PARENTHESIS WITH MIDDLE RING