Yes you can use 'can'. 'May' is slightly more polite or formal, but people mostly use 'can'.

The difference is a question of formality and context. Strictly speaking, 'can' refers to physical ability ( I can swim 100m) , while 'may' refers to permission ('You may leave the class early today'). A generation ago, English speakers still followed this rule. Nowadays, this distinction has virtually disappeared. In spoken English, and in everyday contexts, most native speakers no longer use 'may' for permission. We use 'can' for both types of ability - what we're physically capable of, and also what we're allowed to do. The original use of 'may' - to refer to what is permitted - is still used in formal contexts, however, such as legal documents and official notices. The three sentences you give are all formal English, so the use of 'may' is appropriate. Can you write 'can' instead? Well, if you changed 'may' to 'can' in the notices, the meaning would be the same, but the notices might seem oddly informal. We expect signs and notices to use a certain type of language, and we are used to seeing 'may' for permission in these contexts - 'can' would seem too chatty and conversational. It would be strange to see 'can' on a notice. Here are some examples of can and may: 'Can we park here?' 'I think we can. Oh, look, there's a sign. It says 'You may park here for up to four hours'. Oh, that's good. It's 1 o'clock now, so we can stay here till 5.' As you can see, the formal written sign uses 'may' for permission, but in natural speech the speakers use 'can' to express the same idea.

"may" is used when asking for permission or giving permission. "May I go out, teacher?" "yes you may". It is also used to express possibility "He may come tomorrow, I am not sure".