clear danger emergency escape exit fire keep metal sign text warning doors fire door keep clear no obstruction safety security caution close communicating communication door fire-door information informing keep-clear keep-closed no-obstruction red risk risks risky wording words advice alert appropriate-behavior appropriate-behaviour cars clearway communicate dangerous denied directions law legal no-parking no-standing no-temporary-parking not-allowed not-permitted permission-denied prohibited prohibition refusal restricted restriction restrictions road road-safety road-side signs unacceptable vehicles warning-sign white