Known issue to be fixed in later release. It currently doesn't respect that parameter as it was added after the captcha field in CB AntiSpam was implemented.
forge.joomlapolis.com/issues/5249
You can workaround the issue by using the below CSS to hide it.
Hide All Iocns:
Code:
.cbft_antispam_captcha .cbFieldIcons {
display: none;
}
Hide Required Icon:
Code:
.cbft_antispam_captcha .cbFieldIcons .fa-star {
display: none;
}