diff --git a/README.md b/README.md
index cfe8c18..40c2b7f 100644
--- a/README.md
+++ b/README.md
@@ -829,6 +829,28 @@ It allows you to debug scripts running inside chrome from within Vim.
   comment](https://github.com/puremourning/vimspector/issues/3#issuecomment-576916076)
   for instructions.
 
+# Customisation
+
+There is very limited support for customistaion of the UI. 
+
+## Changing the default signs
+
+Vimsector uses the following signs internally. If they are defined before
+Vimsector uses them, they will not be replaced. So to customise the signs,
+define them in your `vimrc`.
+
+* `vimspectorBP`: A breakpoint.
+* `vimspectorBPDisabled`: A disabled breakpoint
+* `vimspectorPC` The program counter, i.e. current line.
+
+For example, to use some unicode symbols, you could put this in your `vimrc`:
+
+```viml
+sign define vimspectorBP text=🔴 texthl=Normal
+sign define vimspectorBPDisabled text=🔵 texthl=Normal
+sign define vimspectorPC text=🔶 texthl=SpellBad
+```
+
 # FAQ
 
 1. Q: Does it work? A: Yeah, sort of. It's _incredibly_ buggy and unpolished.
diff --git a/python3/vimspector/breakpoints.py b/python3/vimspector/breakpoints.py
index 7e767d0..6e0b76f 100644
--- a/python3/vimspector/breakpoints.py
+++ b/python3/vimspector/breakpoints.py
@@ -52,9 +52,11 @@ class ProjectBreakpoints( object ):
 
     self._next_sign_id = 1
 
-    # TODO: Change to sign_define ?
-    vim.command( 'sign define vimspectorBP text==> texthl=Error' )
-    vim.command( 'sign define vimspectorBPDisabled text=!> texthl=Warning' )
+    if not utils.SignDefined( 'vimspectorBP' ):
+      vim.command( 'sign define vimspectorBP text==> texthl=Error' )
+
+    if not utils.SignDefined( 'vimspectorBPDisabled' ):
+      vim.command( 'sign define vimspectorBPDisabled text=!> texthl=Warning' )
 
 
   def ConnectionUp( self, connection ):
diff --git a/python3/vimspector/code.py b/python3/vimspector/code.py
index 27d9586..4b21192 100644
--- a/python3/vimspector/code.py
+++ b/python3/vimspector/code.py
@@ -50,7 +50,8 @@ class CodeView( object ):
       vim.command( 'nnoremenu WinBar.Restart :call vimspector#Restart()<CR>' )
       vim.command( 'nnoremenu WinBar.Reset :call vimspector#Reset()<CR>' )
 
-      vim.command( 'sign define vimspectorPC text=-> texthl=Search' )
+      if not utils.SignDefined( 'vimspectorPC' ):
+        vim.command( 'sign define vimspectorPC text=-> texthl=Search' )
 
 
   def SetCurrentFrame( self, frame ):
diff --git a/python3/vimspector/utils.py b/python3/vimspector/utils.py
index a9f55df..b04f28f 100644
--- a/python3/vimspector/utils.py
+++ b/python3/vimspector/utils.py
@@ -20,6 +20,8 @@ import contextlib
 import vim
 import json
 import string
+import functools
+
 
 _log_handler = logging.FileHandler( os.path.expanduser( '~/.vimspector.log' ),
                                     mode = 'w' )
@@ -103,7 +105,7 @@ def SetUpHiddenBuffer( buf, name ):
 
 def SetUpPromptBuffer( buf, name, prompt, callback, hidden=False ):
   # This feature is _super_ new, so only enable when available
-  if not int( vim.eval( "exists( '*prompt_setprompt' )" ) ):
+  if not Exists( '*prompt_setprompt' ):
     return SetUpHiddenBuffer( buf, name )
 
   buf.options[ 'buftype' ] = 'prompt'
@@ -467,3 +469,35 @@ def Call( vimscript_function, *args ):
   call += ')'
   _logger.debug( 'Calling: {}'.format( call ) )
   return vim.eval( call )
+
+
+def SignDefined( name ):
+  if Exists( "*sign_getdefined" ):
+    return int( vim.eval( f"len( sign_getdefined( '{ Escape( name ) }' ) )" ) )
+
+  return False
+
+
+MEMO = {}
+
+
+def memoize( func ):
+  global MEMO
+
+  @functools.wraps( func )
+  def wrapper( *args, **kwargs ):
+    dct = MEMO.setdefault( func, {} )
+    key = ( args, frozenset( kwargs.items() ) )
+    try:
+      return dct[ key ]
+    except KeyError:
+      result = func( *args, **kwargs )
+      dct[ key ] = result
+      return result
+
+  return wrapper
+
+
+@memoize
+def Exists( expr ):
+  return int( vim.eval( f'exists( "{ expr }" )' ) )