The little flag icon in the upper right hand corner of a Hub is used to flag the Hub for HubPage violations. HubPage violations include the Hub being written in a language other than English, sexual or inappropriate content, over promotion of a product, poor quality, spamming, etc. I have flagged one or 2 Hubs because they were not written in English.
When a Hub is flagged it is reviewed by the HubPage moderators and can be pulled.
For a more details here is the link to the Learning Center with the "Guidelines for Flagging Hubs".
You used to be able to bookmark Hubs and save them in your account. They removed that feature a few months ago. I think the easiest way to bookmark a Hub is to set up a file "Favorite Hubs" in your browser's bookmarks and save them there. The disadvantage of this system is that you will only be able to retrieve them on the computer you saved them on. If you use multiple computers, it could get complicated.
Here is a link to the forum on the phase out of bookmarks:
Hope this helps. The Learning Center can be a valuable resource for New Hubbers.