You can do watermarks in many applications (Lightroom included) but if you have Windows, an great free app to use is
FastStone Image Viewer.
Open FastStone, create a small (preferably transparent) GIF or PNG with your name, copyright etc in it, put it in a folder somewhere, then attach it to individual images with the handy watermark tool under the FastStone menu Effects > Watermark. Select your watermark image, select the target image, set the opacity, drag the watermark to the location on the image where you want the watermark to appear.
To do watermarks on multiple images in a batch operation, under the FastStone menu go to:
menu Tools > Batch Convert Selected Images > Advanced Options > Watermark.