I don't know how you have it but this is how I put it on my 4.2.2 test site just to test what you are talking about.
prnotice.tpl file
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{if $main eq "catalog" and $current_category.category eq ""}
Powered by X-Cart <a href="
http://www.x-cart.com">{$sm_prnotice_txt}</a>
{else}
Powered by X-Cart {$sm_prnotice_txt}
{/if}
---------------------
Whit this setup the link will be a link only on home page customer side. All other pages including admin will have just text. If you want to have the link as link on all pages including admin just like I said before take out the if statement and leave only the link like this
prnotice.tpl file
----------------
Powered by X-Cart <a href="
http://www.x-cart.com">{$sm_prnotice_txt}</a>
---------------------
It does work as I tested it and it does exactly what it supposed to do - show a clickable link on all pages