diff --git a/src/applications/diffusion/editor/DiffusionRepositoryEditEngine.php b/src/applications/diffusion/editor/DiffusionRepositoryEditEngine.php
--- a/src/applications/diffusion/editor/DiffusionRepositoryEditEngine.php
+++ b/src/applications/diffusion/editor/DiffusionRepositoryEditEngine.php
@@ -287,6 +287,9 @@
       id(new PhabricatorTextEditField())
         ->setKey('callsign')
         ->setLabel(pht('Callsign'))
+        ->setPlaceholder(pht('SOME_UPPERCASE_NAME_NO_SPACES'))
+        ->setControlInstructions(
+          pht('Callsign will become the monogram rXXXXX for this repo'))
         ->setTransactionType(
           PhabricatorRepositoryCallsignTransaction::TRANSACTIONTYPE)
         ->setDescription(pht('The repository callsign.'))
@@ -296,6 +299,9 @@
       id(new PhabricatorTextEditField())
         ->setKey('shortName')
         ->setLabel(pht('Short Name'))
+        ->setPlaceholder('some-lowercase-name-no-spaces')
+        ->setControlInstructions(
+          pht('Short Name will become part of uri\'s for this repo'))
         ->setTransactionType(
           PhabricatorRepositorySlugTransaction::TRANSACTIONTYPE)
         ->setDescription(pht('Short, unique repository name.'))