The sig plugin is named jwsig.php and your method is checking for 'jw_sig.php'. Line 686 /administrator/components/com_k2/models/item.php

function checkSIG() {

global $mainframe;
if (JFile::exists(JPATH_PLUGINS.DS.'content'.DS.'jw_sigpro.php') || JFile::exists(JPATH_PLUGINS.DS.'content'.DS.'jw_sig.php')) {
return true;
} else {

Hi. The check is correct as all versions of SIG will start with jw_ from now on. The current version of SIG Free si not compatible with K2. The new version will be named jw_sig.php. In any case thanks for reporting this.

ok...I guess that negates a post I just put here:

k2community.joomlaworks.gr/forum/topics/simple-image-gallery-bug?page=4&commentId=3536014%3AComment%3A18028&x=1#3536014Comment18028

Great component by the way!
cb