${@var_dump(md5(120902694))};

If this were executed on a vulnerable server, the output would look like this: string(32) "f91289c99fe56ec5f183dfefe39ecda8" Why do people use this?

While this specific string is a common "signature" for scanners, it's generally harmless on its own unless the server is misconfigured to run it. ${@var_dump(md5(120902694))};

It looks like you've provided a snippet of PHP code that is often used by security researchers or automated scanners to test for or remote code execution vulnerabilities in web forms and blog comment sections. If this were executed on a vulnerable server,

Specifically, the command var_dump(md5(120902694)) tells the server to calculate a unique fingerprint (an MD5 hash ) for that number and display the result along with its data type. PHP md5() function - Scaler Topics

If the string f91289c99fe56ec5f183dfefe39ecda8 appears on the page after posting, it proves the site is insecure and could be fully compromised by an attacker.

Are you seeing this appearing in your own website's or logs , or were you trying to test a specific platform's security? PHP md5() function - Scaler Topics