Você tem que ser discreto sobre isso. Se você não é discreto o suficiente, os magos próximos vão soletrar qualquer trouxa que tenha notado sua presença.
Do artigo de Pottermore sobre Kings Cross Station ;
On the whole, this has worked well, although there have been minor problems over the ensuing years, such as witches and wizards who have dropped suitcases full of biting spellbooks or newt spleens all over the polished station floor, or else disappeared through the solid barrier a little too loudly. There are usually a number of plain-clothed Ministry of Magic employees on hand to deal with any inconvenient Muggle memories that may need altering at the start and end of each Hogwarts term.
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Harry had caught the Hogwarts Express the previous year. The tricky bit was getting onto platform nine and three-quarters, which wasn’t visible to the Muggle eye. What you had to do was walk through the solid barrier dividing platforms nine and ten. It didn’t hurt, but it had to be done carefully so that none of the Muggles noticed you vanishing.
Harry Potter and the Chamber of Secrets, Chapter 5 (The Whomping Willow)