As John and Sherlock enter the bank in TBB, we see a red, ‘x’, turn into a green arrow. We go from Sherlock’s face, to a symbol for, 'no’, that becomes a symbol for, 'yes’, or, 'enter’, and then a door opens. I see this as symbolic of Sherlock’s heart. Sherlock has fallen for John, after John shoots the cabbie to save his life, he has made sure he looks handsome and casual in his chair as he waits for John to come home. He lends him his bank card and decides to take a case to make money for John. He is about to introduce John as, 'his friend’, in a very charged situation to a person who appears to be a former lover and is certainly a former friend. This openness will shut down once John corrects him and says that he’s his, 'colleague’, instead. For the rest of TBB, Sherlock will be avoidant and not let John help him at crime scenes. But, right here this is Sherlock’s heart going from closed to open,
In HLV, they will very similarly enter a building, climb escalators and we will see x’s and arrows. However, the order will be reversed,
This coincides with how shut down to love Sherlock is in this scene. He’s about to do something very shrewd with Janine: to trick her into thinking he’s proposing. When confronted about how cold this is, he will bring out the old epithet, 'human error’, and John will be mortified.
Having HLV reference TBB this way closes a thematic loop. We see that Sherlock was open and then shut down in TBB. However, since then we’ve seen him attempt to open up and get shut down and discouraged along the way. In HLV, he’s finally hit bottom with trying: he’s done. John is gone, he has no hope of ever finding love, he’s at his most closed-off and cynical, here. Hence the, 'x’. Notice how the arrow in HLV is pointing at John. That’s where his feelings would go, if he let them.