I Pickpocket Him When He's Annoying.

“Sorry, Sir,” said the young policeman a little nervously. “But Inspector Gregson said no one was allowed in except policemen.”
Holmes nodded graciously. “Of course. I understand completely. Perhaps this will help.” He reached his hand into his pocket and pulled out a small black wallet, opened it, and held it up in front of the young policeman’s face.
“Oh! Oh, Inspector Lestrade, Sir. I’m so sorry, Sir,” stuttered the young man. “And your friend Sir, does he have identification?”
“He is the police surgeon. I’m sure Inspector Gregson would allow him in as well.”
Watson held up his black bag with a smile.
“Yes, Sir, please come in, Sir.”
The policeman opened the door and both Holmes and Watson walked past him into the hall of the dark house.
“Holmes!” exclaimed Watson in a low whisper. “What in heaven’s name?”
Holmes raised a lean, gloved finger to his lips. “Quiet, Watson,” he grinned.
“But how on earth did you –”
The doctor was interrupted by Holmes flipping open the small black wallet and holding it out towards him with a pleased smile.
“Inspector G. Lestrade, Scotland Yard!?” laughed Watson. “Holmes, how did you get this?”
Holmes let out a low chuckle. “I’m afraid I’ve taken to pick pocketing Lestrade, Watson, particularly when he becomes annoying.”