When Marcus and Chantal discuss the opportunity he was offered with the U.S. Marshals, he jokingly comments that "Dr. Bell has a nice ring to it" but he has no interest in enrolling in medical school. Dr. Joseph Bell was a Scottish surgeon and an acquaintance of Arthur Conan Doyle's, and is Doyle's model for the character of Sherlock.
As Holmes and Watson walk to the convention they pass a couple dressed in the 19th century costumes of the characters, though it's the woman dressed as Holmes, deerstalker hat and all.
Sherlock mentions 2 real InCel (Involuntary Celibate) attacks on women when speaking to Art Schultz, the site admin of BlackPill4U.
- "How do you explain one of your members who went on a rampage at their college campus, killing 12 people, mostly women?" While the victim count is off, this likely refers to Elliot Rodger, an admitted InCel who perpetrated the 2014 Isla Vista killings. He murdered his 3 roommates by stabbing, then drove to the campus of University of California at Santa Barbara. He attempted to enter a sorority house to murder the residents, but was thankfully unable to get inside. He then continued his killing spree near the campus by shooting people - mostly women - and mowing them down with his car. He murdered 7 people and injured 14 others. He ended the rampage by crashing his car, after which he committed suicide by gunshot. He left behind a lengthy manifesto and a video explaining that women gave their "affection, and sex and love" to other men but not to him, lamenting his virginity, and promising "retribution" for nearly a decade of "loneliness, rejection and unfulfilled desires".
- "...or the person who opened fire on a group of female engineers in Montreal?" This likely refers to the École Polytechnique massacre aka "the Montreal Massacre". In 1989 Marc Lépine entered the École Polytechnique engineering school and took hostages. He separated the men and women, telling the men to leave and telling the women he was doing this to "fight feminism". He then lined up the women and opened fire on them, killing 6 and injuring 3. He then took to the hallways and entered the cafeteria, killing and injuring women as he went, stabbing to death one woman who asked for medical help. He murdered a total of 14 women, injuring 14 others (women and men) before shooting himself in the head. He left a suicide note with a list of 19 feminists he intended to kill, explaining his belief that feminism ruined his life.
The quote "You know, when it comes to that, I can be the most incurably lazy devil that ever stood in shoe leather" is taken from the first Sherlock-Holmes-Story Arthur Conan Doyle published, "A Study in Scarlet".
This story also features another Scotland Yard Inspector beside Inspector Lestrade, a certain Tobias Gregson. (One of four stories he appears in.)