Wear your bag on your front.
To prevent pickpockets make sure to wear your bag on your front when you are in public spaces and walking on busy streets. During rush hour when there is only standing room left on the bus keep your bag on your front so you can keep an eye on your belongings.
Protect the straps of your bag so that it is not easily yanked out of your hands. Thieves will not risk getting caught by a watchful eye. They target wallets in back pockets and bags casually slung over shoulders or held loosely.
Be watchful, thieves are practiced, quick and silent. You won’t even notice your money or possessions are gone until you get off the bus. You will see that locals always clutch their bags close and in front of them in public spaces as well. Don’t worry about feeling silly wearing your backpack backwards, in San Jose, Costa Rica, doing so is just common sense.