Depending on the type of paper, sign your reproductions with a sharpened pencil (on matte papers) or with an indelible marker (on satin or glossy paper). You should do it in the lower white border outside the image.
Add the number of the series, the date and your signature. You can also add the title of the work if you want. You can do it in many formats. I invite you to look for some examples in Google, but here I show you how I label my limited editions.
Be clear how you want to label your works from the beginning. You must be consistent with this format.
All this and many more secrets in my blog: https://www.pakocampo.com/giclee-prints-step-by-step/
And do not forget to stop by my store at https://www.pakocampo.com/shop!