If you have ShopSite v9.0 or newer this is pretty easy in your custom search template using the SearchResultCount template tag added in that version, see the custom search template spec at:
http://www.shopsite.com/help/9.0/en-US/sc/pro/custom.template.spec-search.html
I've not used this tag personally in a custom search template (so consider this pseudo-code that you will test yourself), but I would imagine you could use this code something like:
[-- IF SearchResultCount "0" --]
No results for the search: [-- SEARCHSTRING --]
[-- ELSE --]
There were [-- SearchResultCount --] results for the search: [-- SEARCHSTRING --]
[-- END_IF --]
If you have an older version of ShopSite, then the only way I know of to get the count by setting a VAR to 0 before the LOOP SEARCH loop and incrementing it in the loop whenever a product result is incountered, then after the END_LOOP SEARCH you can check your VAR, if it is still 0 then there were no results, otherwise there wete results. So perhaps something like this:
[-- VAR.searchresultscounter 0 --]
<table border="1">
[-- LOOP SEARCH --]
[-- IF SEARCHPRODUCT --]
<td>Product:</td>
[-- VAR.searchresultscounter INC --]
[-- END_IF --]
[-- IF SEARCHLINK --]
<td>Link:</td>
[-- END_IF --]
[-- SEARCHRESULT --]
[-- END_LOOP SEARCH --]
</table>
[-- IF VAR.searchresultscounter "0" --]
No results for the search: [-- SEARCHSTRING --]
[-- ELSE --]
There were [-- VAR.searchresultscounter --] results for the search: [-- SEARCHSTRING --]
[-- END_IF --]
-Loren