Section 10A. Whoever wears the uniform, or any distinctive part thereof, of the United States army, navy, marine corps, revenue cutter service, or coast guard, or of the national guard, or of any organization enumerated in section seventy of chapter two hundred and sixty-six, or wears a hat, cap or other apparel similar to or resembling the hat, cap or other distinctive part of any such uniform, while engaged, for personal profit, in soliciting alms, in selling merchandise or taking orders for the same, in seeking or receiving contributions in support of any cause, enterprise or undertaking or in soliciting or receiving subscriptions to any book, paper or magazine, shall be punished by a fine of not more than one hundred dollars, or by imprisonment for not more than three months; provided, that this section shall not apply to the sale of property or any other act or transaction conducted under authority of the government of the United States, and provided further, that no person shall be subject to prosecution hereunder for wearing the uniform, or any distinctive part thereof, while engaged as aforesaid, of any organization enumerated in said section seventy if he so acted under authority of such organization or any post, camp or other unit thereof.