Welcome to  (Citation to come.), a little reminder message to alert you that a reference is still desired at a particular insertion point within the article.
Ref2Come is simply a reminder and/or alert that a citation / reference is still desired or required at or near the particular insertion point in the article where the (Citation to come.) phrase is displayed.
Place the following code somewhere in a wiki article:
The phrase "Citation to come." will appear wherever you insert the code as shown above.
- ↑ (Citation to come.)