See net-im/ricochet as an example. It installs icons and INSTALLS_ICONS=yes is currently missing.
A commit references this bug: Author: marcus Date: Sun Jul 24 14:24:34 UTC 2016 New revision: 419006 URL: https://svnweb.freebsd.org/changeset/ports/419006 Log: Update to 2.17.4. * Check PLIST_FILES for icons [1] * Add VARS and VARS_OFF to the option helper list [2] * Add NO_ARCH [2] PR: 211175 [1] Submitted by: koobs [2] Changes: head/ports-mgmt/portlint/Makefile head/ports-mgmt/portlint/src/portlint.pl
Fixed in 2.17.4.