a 5-yen coin

When my friend came to Japan, he asked me, which coin it was and show the 5-yen coin. I told him, it was 5-yen and asked him, why he couldn't recognise it. I didn't expect the reason, he told me there was no number. A-ha, I didn't know that, yes, it only had the number in Kanji. Perhaps, Chinese people could recognise it but it might have been hard for westerners. If you found the golden coin has a hole on the centre, it is definitely 5-yen coin in Japan.