You may notice this CrossMark symbol on the PDF of a recent journal article you have downloaded. The icon is linked to information about this journal article, and keeps you updated with any changes even though you have downloaded the PDF to your own computer, as long as you are connected to the internet. You may also see it on the HTML of an article. The CrossMark icon link will most likely tell you that the version of the journal article you are viewing is current, but it will also warn you if there have been updates to the article, then link to those updates.
The DOI (digital object identifier) registration service CrossRef has developed the CrossMark service for use by publishers who use CrossRef DOIs. See CrossMark examples implemented by a variety of publishers.