Ok. So Ive somehow managed to sort this issue...
For anyone having the same problem here is how I sorted it... (Im using an iMac so can only give the options I have, don't know about Windows)
I can only assume that LR5 automatically applies your watermark to all imported photos, therefore when emailing a photo from LR the watermark is present.
To remove it, once you've done your relevant editing to the photo, whilst viewing the photo in question, go to Develop, and when in that function you go to Lightroom (in the top bar) - Edit Watermarks.
Once in there, I saw that the Custom watermark was already selected. I edited that watermark simply by going to Watermark Effects, and putting the Opacity to zero. Saved that as 'Email' or call it what you want.
I then, whilst still in Develop, went through the same process: Lightroom - Edit Watermark, and selected the 'Email' watermark, and clicked Done.
I then selected the Library function and went to File - Email Photo... and it worked! Sounds simple I know but didn't seem that obvious before, or whatever order I was changing the watermark, editing and emailing just wasn't working.
Hope this helps.
The watermark is there because it is selected in the Export dialog, it is not applied on import as Lightroom is a non-destructive image processor and never alters the image..
To disable it go to File->Export then deselect the Watermark option.
Then whenever you use the email option it wont appear, but if you wish to watermark on export remember to reselect it and select the right watermark.
That is right. The OP needs to double check the export settings and make sure the watermark is not checked.
Thank you BKKDon & JimHess, a far easier way of sorting the problem!
I'd seen previous posts saying once an item had been watermarked, it was there forever, glad it we managed to sort it!