Otoshidama tend to be given in white envelopes bound with a pink or red paper 'ribbon cord' (in mizuhiki style). Often this "ribbon cord" may just be a pattern printed on the envelope. Money bills are usually folded in threes before being inserted.
The word "お年玉" (otoshidama) may sometimes be printed on the front of the envelope. This unambiguously identifies this as otoshidama (instead of hongbao). A less common word is "祝".
