Japan has four-ish writing systems: hiragana, katakana, romanji, and kanji.

Hiragana（ひらがな）: these curly little guys are used for phonetic spellings of words and to glue sentences together.
Katakana（カタカナ）: these represent the exact same syllables as hiragana, but with sharp, angular symbols to make them more masculine. At least, that’s how it started out, but now katakana are mostly used to spell out foreign loan words and onomatopoeia like “kaboom.”
Romaji（ローマ字）: Roman or “English” letters, because you’re also expected to be able to read these in today’s modern, international society.
Kanji　(漢字): The big, complex, many-lined ideograms adopted and modified from Chinese. These number in the thousands and defeat even the most dedicated students of Japanese. We’ll just look at 15 today.

A lot of signs and controls in Japan are written in Kanji. Thankfully, there’s some which you see more often than others. Here’s my select, chef’s choice, useful Kanji for tourists along with some handy mnemonics for decoding them. Some come in pairs, and some are loners.

大 (Big) & 小 (Small)

You can find this pair on controls for lights, speakers, and faucets. How much light/sound/water do you want? Big or small? Big is, well… big (大). Look at him… he’s standing with his arms out. His legs are bent because of forced perspective; he’s so tall you’re looking up at him. But small? He’s just a little guy (小). His arms are tucked in. He’s trying to stay out of big’s way.

止 (Stop, Don’t)

Sometimes, there are places you shouldn’t go, or things you need to stop. Not supposed to go in a door? It will have this guy on it. Need to turn off the bidet on a toilet? Press the button with this on it. Watch out for this guy, standing by a post on the road with his arm out (止). He’ll let you know when it’s time to stop.

開 (Open) & 閉 (Close)

In Japan, a big person is a well-behaved person (大人しい). Responsible people can be trusted with elevator door controls which actually work. Newer controls often have universal, arrow-based symbols on them, but older Showa-era elevators and other doors with class still use kanji. So, what’s a door? It’s also a gate (門). When the gate is open, you can hang a nice, inviting lantern in it (開) to show it’s open. When it’s closing time, you smash that lantern as you close the gate. Now the lantern is smaller and mangled (閉). Whoops!

入 (Enter) & 出 (Exit)

Train stations have lots of these… sometimes too many. Somebody is running fast to catch their train. They’re going so fast, there’s motion blur (入)… that’s what happens when you have to find the entrance (入り口) while you’re running late. After you’ve gotten back, it’s time to exit. But now your hands and even legs have shopping bags hanging from them (出)… it was a crazy day. Time to find an exit (出口) and go home.

上 (Up) & 下 (Down)

Japan loves escalators. There’s a lot of people to move around trains, subways, and shopping malls, and they can’t all take the elevator. Sometimes there’s even too many people to see what goes where, but these mark what goes up and down. Our friend the guard is holding his hand out above ground to show us what’s up (上). They flip him upside-down when it’s time to go down, and his arm hangs at an angle (下).

円 (Yen)

This is the marker at the end of a number to show it’s a price. Like that hat? It’s only 2000円. That’s a pretty good price. Look at this nerd, with his big square glasses on, staring at all the prices. He’s trying to find the best deal on Gundam kits to take back home.

肉 (Meat)

I like restaurants with this character on the sign. There’s some good eating - look at those ribs (肉).

水 (Water)

Overwhelmed by the choices in a vending machine? Just thirsty? Get some water. A gentle stream of nice, pure water, flowing between two banks (水).

車 (Car)

Looking for a car? Need to get somewhere? Look for a rickshaw. Two wheels and a seat (車) is all you really need to get where you’re going. Unless you add electricity, in which case you get a train (電車).

Bonus:

自動 (Automatic)

Things that move (動) themselves (自) are automatic. This is plastered on a lot of doors… but sometimes you have to actually touch the door where it says this to get it to open (開). It’s automatic… but only kind of. This is a tricky one and I don’t have a fun mnemonic. But if you’re stuck in front of a door that won’t open see this on a part of the door, it’s probably a control to get it to open.