diff --git a/src/ai/api/ai_sign.cpp b/src/ai/api/ai_sign.cpp
--- a/src/ai/api/ai_sign.cpp
+++ b/src/ai/api/ai_sign.cpp
@@ -30,7 +30,7 @@
 {
 	EnforcePrecondition(false, IsValidSign(sign_id));
 	EnforcePrecondition(false, !::StrEmpty(name));
-	EnforcePreconditionCustomError(false, ::strlen(name) < MAX_LENGTH_SIGN_NAME_BYTES, AIError::ERR_PRECONDITION_STRING_TOO_LONG);
+	EnforcePreconditionCustomError(false, ::Utf8StringLength(name) < MAX_LENGTH_SIGN_NAME_CHARS, AIError::ERR_PRECONDITION_STRING_TOO_LONG);
 
 	return AIObject::DoCommand(0, sign_id, 0, CMD_RENAME_SIGN, name);
 }
@@ -66,7 +66,7 @@
 {
 	EnforcePrecondition(INVALID_SIGN, ::IsValidTile(location));
 	EnforcePrecondition(INVALID_SIGN, !::StrEmpty(text));
-	EnforcePreconditionCustomError(false, ::strlen(text) < MAX_LENGTH_SIGN_NAME_BYTES, AIError::ERR_PRECONDITION_STRING_TOO_LONG);
+	EnforcePreconditionCustomError(false, ::Utf8StringLength(text) < MAX_LENGTH_SIGN_NAME_CHARS, AIError::ERR_PRECONDITION_STRING_TOO_LONG);
 
 	if (!AIObject::DoCommand(location, 0, 0, CMD_PLACE_SIGN, text, &AIInstance::DoCommandReturnSignID)) return INVALID_SIGN;
 
diff --git a/src/signs_cmd.cpp b/src/signs_cmd.cpp
--- a/src/signs_cmd.cpp
+++ b/src/signs_cmd.cpp
@@ -40,7 +40,7 @@ CommandCost CmdPlaceSign(TileIndex tile,
 	if (!Sign::CanAllocateItem()) return_cmd_error(STR_ERROR_TOO_MANY_SIGNS);
 
 	/* Check sign text length if any */
-	if (!StrEmpty(text) && strlen(text) >= MAX_LENGTH_SIGN_NAME_BYTES) return CMD_ERROR;
+	if (!StrEmpty(text) && Utf8StringLength(text) >= MAX_LENGTH_SIGN_NAME_CHARS) return CMD_ERROR;
 
 	/* When we execute, really make the sign */
 	if (flags & DC_EXEC) {
@@ -80,7 +80,7 @@ CommandCost CmdRenameSign(TileIndex tile
 
 	/* Rename the signs when empty, otherwise remove it */
 	if (!StrEmpty(text)) {
-		if (strlen(text) >= MAX_LENGTH_SIGN_NAME_BYTES) return CMD_ERROR;
+		if (Utf8StringLength(text) >= MAX_LENGTH_SIGN_NAME_CHARS) return CMD_ERROR;
 
 		if (flags & DC_EXEC) {
 			/* Delete the old name */
diff --git a/src/signs_gui.cpp b/src/signs_gui.cpp
--- a/src/signs_gui.cpp
+++ b/src/signs_gui.cpp
@@ -50,8 +50,8 @@ struct SignList {
 	static const Sign *last_sign;
 	GUISignList signs;
 
-	char filter_string[MAX_LENGTH_SIGN_NAME_BYTES]; ///< The match string to be used when the GUIList is (re)-sorted.
-	static bool match_case;                         ///< Should case sensitive matching be used?
+	char filter_string[MAX_LENGTH_SIGN_NAME_CHARS * MAX_CHAR_LENGTH]; ///< The match string to be used when the GUIList is (re)-sorted.
+	static bool match_case;                                           ///< Should case sensitive matching be used?
 
 	/**
 	 * Creates a SignList with filtering disabled by default.
@@ -109,7 +109,7 @@ struct SignList {
 	static bool CDECL SignNameFilter(const Sign * const *a, FilterInfo filter_info)
 	{
 		/* Get sign string */
-		char buf1[MAX_LENGTH_SIGN_NAME_BYTES];
+		char buf1[MAX_LENGTH_SIGN_NAME_CHARS * MAX_CHAR_LENGTH];
 		SetDParam(0, (*a)->index);
 		GetString(buf1, STR_SIGN_NAME, lastof(buf1));
 
@@ -146,7 +146,7 @@ struct SignListWindow : QueryStringBaseW
 	int text_offset; ///< Offset of the sign text relative to the left edge of the SLW_LIST widget.
 	Scrollbar *vscroll;
 
-	SignListWindow(const WindowDesc *desc, WindowNumber window_number) : QueryStringBaseWindow(MAX_LENGTH_SIGN_NAME_BYTES)
+	SignListWindow(const WindowDesc *desc, WindowNumber window_number) : QueryStringBaseWindow(MAX_LENGTH_SIGN_NAME_CHARS * MAX_CHAR_LENGTH, MAX_LENGTH_SIGN_NAME_CHARS)
 	{
 		this->CreateNestedTree(desc);
 		this->vscroll = this->GetScrollbar(SLW_SCROLLBAR);
@@ -155,7 +155,7 @@ struct SignListWindow : QueryStringBaseW
 
 		/* Initialize the text edit widget */
 		this->afilter = CS_ALPHANUMERAL;
-		InitializeTextBuffer(&this->text, this->edit_str_buf, MAX_LENGTH_SIGN_NAME_BYTES, MAX_LENGTH_SIGN_NAME_PIXELS); // Allow MAX_LENGTH_SIGN_NAME_BYTES characters (including \0)
+		InitializeTextBuffer(&this->text, this->edit_str_buf, MAX_LENGTH_SIGN_NAME_CHARS * MAX_CHAR_LENGTH, MAX_LENGTH_SIGN_NAME_CHARS, MAX_LENGTH_SIGN_NAME_PIXELS);
 		ClearFilterTextWidget();
 
 		/* Initialize the filtering variables */
@@ -462,7 +462,7 @@ enum QueryEditSignWidgets {
 struct SignWindow : QueryStringBaseWindow, SignList {
 	SignID cur_sign;
 
-	SignWindow(const WindowDesc *desc, const Sign *si) : QueryStringBaseWindow(MAX_LENGTH_SIGN_NAME_BYTES)
+	SignWindow(const WindowDesc *desc, const Sign *si) : QueryStringBaseWindow(MAX_LENGTH_SIGN_NAME_CHARS * MAX_CHAR_LENGTH, MAX_LENGTH_SIGN_NAME_CHARS)
 	{
 		this->caption = STR_EDIT_SIGN_CAPTION;
 		this->afilter = CS_ALPHANUMERAL;
@@ -488,7 +488,7 @@ struct SignWindow : QueryStringBaseWindo
 		*last_of = '\0';
 
 		this->cur_sign = si->index;
-		InitializeTextBuffer(&this->text, this->edit_str_buf, this->edit_str_size, MAX_LENGTH_SIGN_NAME_PIXELS);
+		InitializeTextBuffer(&this->text, this->edit_str_buf, this->edit_str_size, this->max_chars, MAX_LENGTH_SIGN_NAME_PIXELS);
 
 		this->SetWidgetDirty(QUERY_EDIT_SIGN_WIDGET_TEXT);
 		this->SetFocusedWidget(QUERY_EDIT_SIGN_WIDGET_TEXT);
diff --git a/src/signs_type.h b/src/signs_type.h
--- a/src/signs_type.h
+++ b/src/signs_type.h
@@ -17,7 +17,7 @@ struct Sign;
 
 static const SignID INVALID_SIGN = 0xFFFF;
 
-static const uint MAX_LENGTH_SIGN_NAME_BYTES  =  31; ///< The maximum length of a sign name in bytes including '\0'
+static const uint MAX_LENGTH_SIGN_NAME_CHARS  =  31; ///< The maximum length of a sign name in characters including '\0'
 static const uint MAX_LENGTH_SIGN_NAME_PIXELS = 255; ///< The maximum length of a sign name in pixels
 
 #endif /* SIGNS_TYPE_H */