signal in不是固定搭配,而sign in是固定搭配.
signal在当不及物动词讲时可以和介词连接：
vi.
发信号；用信号联络；用信号通讯：
to signal with flags
用旗语发信号
to signal for help
发信号求救
break up是固定搭配,意思是打碎,破碎；结束；解散；衰落
但是没有说是加上about是固定搭配,而是介词或者连词的基本用法,用来引出后面的关于的人或者物.
The party has broken up into several splinter groups.
该党已分裂成几个派别.
to break up under the strain
因过劳而身体垮掉
She broke them up out of jealousy.
出于嫉妒之心,她离间了他们的关系.
Break up into（分解为）和Break up with（分手,断绝关系）是固定用法,例如
Without a strongman,Iraq could break up into three weak and warring ethnic states.
It may be time to break up with online dating and try meeting someone the old-fashioned way:In person.
