So Mycrofts phone call in The Sign of Three is seen to show him warning Sherlock not to get involved, but what if he was trying to keep Sherlock calm?
After all we see Molly worrying to Lestrade saying ‘So he’ll have to make a speech.In front of people, with actual people there , actually listening’ , to which Lestrade replies with trepidation ‘well… whats the worse that could happen…’ after which its implied his brain will go to mush (‘Helen Lousie probably thought the same’). Sherlock has a very , very good memory so it wont go to mush due to that , it’ll go due to nerves.
And we see this at the start of Sherlock’s speech, he’s stuttering and nervous and unsure what to say. The only time we’ve really seen him stutter that I can remember is in Scandal in Belgravia , and that was when he was uneasy about the enviroment he was in (Irene was naked and he couldn’t deduce anything from her). So he must have been nervous , he didn’t want to mess up his speech for an honour which his only best friend (the human kind at least) has betowed on him, we know he doesn’twant to mess it up, when he think he has by making people cry he immedietly seems worried ‘John? John did I do it wrong?’. Except this time he apparently doesn’t need to think of Redbeard perhaps due to Johns hug.
But I genuinely think that Mycroft was trying to keep Sherlock calm, he knows how important John is to Sherlock , so knows that Sherlock will be scared or anxious at the very least. After all Mycroft wants to look after his baby brother.