The trial of Ross W. Ulbricht, a California man charged with running an online black-market bazaar called Silk Road, had barely begun when an unusual objection was lodged.

At issue was a piece of information that Mr. Ulbricht’s lawyer suggested was critically important, yet was omitted by federal prosecutors: an emoji.

And not just any emoji, or emoticon, as the symbol is sometimes called — it was the gold standard. A version of a smiley face.

The unusual debate, taking place out of the presence of the jury in Federal District Court in Manhattan, arose after a prosecutor finished reading the text of an Internet post. “I’m so excited and anxious for our future, I could burst,” the prosecutor had read to the jury, making no mention of the smiling symbol that followed.