The church is of course a corporate body...the Bride of Christ, etc. But...it is also composed of individual believers, who are charged with the responsibility of sharing their faith with others.
IMO, this sign, though true, could hamper individual efforts to witness. And I simply don't see the need to do that in this case.
Oh, the tightrope we have to walk..."Speaking the truth in love" is easily said, but not-so-easily done. Some struggle with making the "truth" part plain. Others have trouble with the "love" part. Still others, IMO, do the "love" part, but have difficulty expressing it.