Uitype 10 don't show label
If you create a relation field with UIType 10 and you configured multiple modules, it won't show the field label.
This was a decision, because the dropdown could be very long, which don't fit in this label box.
But if this isn't a problem in your system, you could do the following:
Open file: layouts/vlayout/moduels/Vtiger/EditViewBlocks.tpl
Search:
{if $REFERENCE_LIST_COUNT > 1}
Insert after this line:
<label class="muted pull-left" style="margin-bottom:0;line-height:27px;">{vtranslate($FIELD_MODEL->get('label'), $MODULE)}</label>