How to tell Simplified and Traditional Chinese apart? Imagine that I know nothing about the language. I open a book and look at some Chinese text. 

What’s the easiest (and deterministic) way to tell if I'm looking at simplified or traditional Chinese? 

Are there any common radicals that appear in one and not the other?
Some regular simplification rules:

釒(金)→钅: 針→针, 鈴→铃
飠(食)→饣: 飲→饮, 飯→饭
糹(糸)→纟: 紅→红, 絲→丝
訁(言)→讠: 計→计, 語→语

貝→贝: 貨→货, 貴→贵
見→见: 視→视, 現→现
頁→页: 項→项, 題→题
東→东: 陳→陈, 棟→栋
車→车: 軟→软, 輩→辈
門→门: 問→问, 閑→闲
烏→乌: 鎢→钨, 塢→坞
魚→鱼: 漁→渔, 魯→鲁
鳥→鸟: 鴨→鸭, 鷹→鹰
馬→马: 媽→妈, 騰→腾

There are also some simplified examples of complex components:

爿→丬: 壯→壮, 將→将
豐→丰: 灃→沣, 艷→艳
風→风: 瘋→疯, 諷→讽
長→长: 張→张, 帳→帐
堯→尧: 燒→烧, 饒→饶
䜌→亦: 戀→恋, 彎→弯
睪→: 澤→泽, 驛→驿
炏→艹: 營→营, 榮→荣
蘭→兰: 欄→栏, 爛→烂
羅→罗: 蘿→萝, 邏→逻
買→买: 買→买, 賣→卖
產→产: 鏟→铲, 滻→浐
齊→齐: 擠→挤, 濟→济
幾→几: 機→机, 譏→讥
柬→拣(the right part): 煉→炼, 練→练
盧→户: 廬(广+～)→庐(广+户), 驢(馬+～)→驴(马+户)
盧→卢: 鱸(魚+～)→鲈(鱼+卢), 顱(～+頁)→颅(卢+页)
戔→戋: 錢→钱, 棧→栈
咼→呙: 鍋→锅, 窩→窝
樂→乐: 爍→烁, 櫟→栎
豈→岂: 鎧→铠, 凱→凯
肅→肃: 蕭→萧, 嘯→啸

There are also many irrational simplifications, such as cursive writing, or homophonic substitution, and some characters are combined by these simplified components. If you see Chinese characters with a lot of these parts, you can be sure that this is traditional Chinese.