CHG_CANON wrote:
Set-up a LR Export preset that implements a watermark. Set-up separate Export Presets for each / every type of sharing, using unique export target folders. Upload / share images only from these purpose-specific folders, that is one for Instagram, one for Facebook, one for UHH, and so forth. Invest 'thought' in the set-up and then you don't have to 'think' each time you want to quickly create an image for sharing based on all the appropriate resolution, quality, and watermark settings.
If you use the site that allows downloading placing a watermark across the bottom is really useless. Trivial PS can remove the watermark faster than it takes for you to upload the photo. Simple fact of life. You either post a lower resolution file so it's not worth stealing or you put an opaque watermark through the middle. In either of those cases the visual quality is probably less than than you want. If concerned find a site that does not allow download.