Indeed, no one seemed to notice. Luckily they were on a sidewalk sort of out of the way of the general crowd as well. During all of the conversation between the three Silas attempted to put something in his inventory, which would require him to use the command and stealthily put it in there in a way that would not alert the other two to him seemingly hiding things from them. 

---
Silas Hiding the Paper: 47 - 7 Sleight of Hand = 40

Sasha Observation: 21 - 16 Observation = 5

Mike Observation: 68 - 18 Observation = 50
---

Silas was stealthy enough with both his silent muttering of the Inventory command and sliding the piece of paper into his inventory for Mike to have missed it, but Sasha would have been able to notice Silas holding the note for a moment before it vanished from his hand, which was a highly likely sign of someone putting something into their inventory.