Edited version of Kelly’s method:
1) Find a sign or map with both the English and Japanese versions and take a photo of it for future use.
2) Flex your creative brain muscles and equate symbols to familiar pictures.

For example, in the sign below, the first character looks like a P9 and the second character looks like a ladder on the left side. The second to last character looks like Gumby with the letter J, while the last character looks like a house.

So far, we have used the letter J, the letter R, a power line, a person, a house, two flags surrounding a hut, and a disc golf hole, just to name a few.  Some of the simpler Japanese characters also look like Hebrew letters.