Can anybody read my birdbath?

Last year, my son found a little ceramic dish half-buried in the garden. We've been using it as a birdbath ever since.

What's interesting about this little dish is that it has two large Chinese characters on the inner surface. I did Japanese classes a few years ago, so I know a few basic Kanji, but these one's aren't familiar to me. Here's a photo of the birdbath, taken just after it was excavated, showing the characters.

[caption id="attachment_23" align="alignnone" width="240" caption="Can anyone tell me what this means?"][/caption]

If anyone knows what this means, please leave a comment. I hope it's not something along the lines of the tattoo, allegedly popular with American servicemen stationed in Japan after the Second World War, that read "I'm too stupid to ask what this means."

Updated I've uploaded a clearer picture of the birdbath, without the shadow that obscured the second character in the original image.