A large portion of tourists do know there are protests in Hong Kong lasting for a few weeks and it's about the extradition bill, where criminals as defined in both Hong Kong and mainland at the same time could be transferred to Beijing with Hong Kong judges' approval. These are publicly reported in mainland. It's useless just retelling the story itself, or even worse in a sense of superiority (as pointed out in a twitter comment) saying "did you know? oops, sorry for you".
I think open-minded mainland people would prefer a thorough and better explanation of the opposition. Because from many ordinary people's perspective, Hong Kong still keeps legal control over the extradition under the bill and it would help the fight against corruption since Hong Kong is regularly involved in economic crimes committed by mainland citizens. "Extradition bill threatens your property in Hong Kong", appearing in many flyers, just looks like some kind of evidence supporting it for ordinary people.
Also, mainland people worries about stability and order of Hong Kong as much as protesters concern about freedom and democracy. Even if they disagree with each other on the order of importance, protesters could express a little about the shared value for long-term law and order in Hong Kong to dispel some concerns. Stressing only on freedom towards mainland people sounds as horrible as stressing only on order towards protesters, let alone storming the building of Legislative Council or attacking the police with bricks.
As is well known to mainland people, in the colonial era, the Hong Kong governor was appointed by British monarch and no democratic legitimacy existed until Britain started preparing the handover to China in 1980s. There were also multiple bloody riots crushed in the colonial history. It's really confusing for tourists to see protesters weaving flags of colonial or British flags without further clarification, for what these flags stand for besides asking for Britain's direct interference.
Lastly, truth is powerful enough. There is no need to exaggerate the numbers.