So I bought the legendary edition of skyrim on my PC, and the shadowmarks for the thieves guild are not appearing.

I have no mods or anything installed. just the legendary edition.

Please help

Have you installed the Unofficial patches as well ??? http://afkmods.iguanadons.net/index.php?/files/category/95-unofficial-patch-project/

After that verify your game cache files https://support.steampowered.com/kb_article.php?ref=2037-QEUH-3335

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There is a mod too: http://www.nexusmods.com/skyrim/mods/10056/?

have you done the thieves guild yet?

as far as I am aware the Cache shadow marks only appear after you have done that cities "special job"