航空标志 meaning in English

aerial sign

All air mail items must bear the superscription " by air mail "
航空标志所有空邮件均必须注明" byairmail (空邮)字样。
In the case of parcels an air mail label must also be affixed to the despatch note if one is used
若邮件是须填写发递单的包裹,还须将航空标志贴在单上。
The label should be affixed to the top left hand corner of the address side of the envelopes or close to the address on parcels and packets ( close to each address if it is shown in more than one place on the item )
在投寄时须将蓝色的航空标志贴在信封有地址一面的左上角，或在包裹或邮包接近地址的地方(如超过一个，应在接近地址的地方) 。