The inscription to be found on the edge both of the UK's 'Welsh' £1 coins - 'leek', issued in 1985 and 1990 and 'dragon', issued in 1995 and 2000. It means 'True am I to my country' and comes from the chorus of the Welsh National Anthem:
Gwlad! Gwlad! Pleidiol wyf i'm gwlad,
Tra môr yn fur l'r bur hoff bau,
O, bydded i'r hen iaith barhau!
A rather free translation of which is:
Wales! Wales! O but my heart is with you!
And long as the sea
Your bulwark shall be
To Cymru my tongue shall be true.
I find it interesting that while the Royal Mint translates Gwlad as 'my country', the Welsh translate it as Wales. Devolutionary tension, anyone? (As others have pointed out, 'Gwlad' is Welsh for 'country', while 'Cymru' is welsh for Wales itself. I was only pointing out the discrepancy, since the Royal Mint is suggesting that the Welsh are referring to The United Kingdom of Great Britain and Northern Ireland, when they are more probably referring just to their corner of it.
For those of you wondering about pronunciation (and I don't blame you), here is a rough guide: 'Play-deeol oo-eev eem gwlard'.
http://www.google.com/search?q=cache:DBqHgHgOy-wC:www.pen-y-ffordd.co.uk/anthem.htm+Pleidiol+Wyf+I%27m+Gwlad+pronunciation&hl=en
http://www.royalmint.com/talk/pounddesigns.asp
http://www.celticmist.freeserve.co.uk/henwlad.htm